Functions are objects in JavaScript, as you should know by now, if you have read any of the prerequisite articles. And as objects, functions have methods, including the powerful ApplyCalland Bind methods. On the one hand, Apply and Call are nearly identical and are frequently used in JavaScript for borrowing methods and for setting the this value explicitly.

We also use Apply for variable-arity functions; you will learn more about this in a bit. Receive Updates Email Address: On the other hand, we use Bind for setting the this value in methods and for currying functions. We use the Bind method primarily to call a function with the this value set explicitly. It other words, bind allows us to easily set which specific object will be bound to this when a function or method is invoked.

The need for bind usually occurs when we use the this keyword in a method and we call that method from a receiver object; in such cases, sometimes this is not bound to the object that we expect it to be bound to, resulting in errors in our applications.

It will become clear like teardrop in a moment. Before we look at the code for this section, we should understand the this keyword in JavaScript. When you click the button, you get an error because this in the clickHandler method is bound to the button HTML element, since that is the object that the clickHandler method is executed on.

Set a default parameter value for a JavaScript function - Stack Overflow

This particular problem is quite common in JavaScript, and JavaScript frameworks like Backbone. To fix the problem in the preceding example, we can use the bind method thus: Instead of this line:.

Consider this other way to fix the this value: You can pass an anonymous callback function to the click method and jQuery will bind this inside the anonymous function to the button object.

JavaScript - Functions

The this value is also bound to another object if we assign the method where this is defined to a variable. When we execute the showDataVar function, the values printed to the console are from the global data array, not the data array in the user object.

This happens because showDataVar is executed as a global function and use of this inside showDataVar is bound to the global scope, which is the window object in browsers. In JavaScript, we can pass functions around, return them, borrow them, and the like. And the bind method makes it super easy to borrow methods. One problem with this example is that we are adding a new method showData on the cars object and we might not want to do that just to borrow a method because the cars object might already have a property or method name showData.

As we will see in our discussion of Apply and Call below, it is best to borrow a method using either the Apply or Call method. Function Curryingalso known as partial function applicationis the use of a function that accept one or more arguments that returns a new function with some of the arguments already set. The function that is returned has access to the stored arguments and variables of the outer function. First we have a simple greet function that accepts 3 parameters:.

And we use the bind method to curry preset one or more of the parameters our greet function. The first argument of the bind method sets the this value, as we discussed earlier:. When we use the bind method for currying, all the parameters of the greet function, except the last rightmost argument, are preset. So it is the rightmost argument that we are changing when we call the new functions that were curried from the greet function.

Again, I discuss currying at length in a separate blog post, and you will see how we can easily create very powerful functions with Currying and Compose, two Functional JavaScript concepts.

So, with the bind method, we can explicitly set the this value for invoking methods on objects, we can borrow and copy methods, and assign methods to variable to be executed as functions. And as outlined in the Currying Tip earlier, you can use bind for currying.

The Apply and Call methods are two of the most often used Function methods in JavaScript, and for good reason: In addition, the apply function in particular allows us to execute a function with an array of parameters, such that each parameter is passed to the function individually when the function executes—great for variadic functions; a variadic function takes varying number of arguments, not a set number of arguments as most functions do.

Just as in the bind example, we can also set the this value when invoking functions by using the Apply or Call methods. The first parameter in the call and apply methods set the this value to the object that the function is invoked upon.

Here is a very quick, illustrative example for starters before we get into more complex usages of Apply and Call:. Note that the first argument to call sets the this value. In the preceding example, it is set to the gameController object. The other arguments after the first argument are passed as parameters to the avg function. The apply and call methods are almost identical when setting the this value except that you pass the function parameters to apply as an array, while you have to list the parameters individually to pass them to the call method.

More on this follows. Use Call or Apply To Set this in Callback Functions I borrowed this little section from my article, Understand JavaScript Callback Functions and Use Them. The Apply method sets the this value to callbackObj. This allows us to execute the callback function with the this value set explicitly, so the parameters passed to the callback function will be set on the clientData object:.

The Apply, Call, and Bind methods are all used to set the this value when invoking a method, and they do it in slightly different ways to allow use direct control and versatility in our JavaScript code. The this value in JavaScript is as important as any other part of the language, and we have the 3 aforementioned methods are the essential tools to setting and using this effectively and properly.

The most common use for the Apply and Call methods in JavaScript is probably to borrow functions. We can borrow functions with the Apply and Call methods just as we did with the bind method, but in a more versatile manner.

An array-like object is an object that has its keys defined as non-negative integers. It is best to specifically add a length property on the object that has the length of the object, since the a length property does not exist on objects it does on Arrays. I should note for clarity, especially for new JavaScript developers that in the following examples, when we call Array.

And it is from there—the source—that we are borrowing the Array methods. Hence the use of code like Array. Keep in mind the array-like object is a real object, it is not an array at all:. We get all the great benefits of an object and we are still able to use Array methods on our object, when we setup our object as an array-like object and borrow the Array methods.

All of this is made possible by the virtue of the call or apply method. The arguments object that is a property of all JavaScript functions is an array-like object, and for this reason, one of the most popular uses of the call and apply methods is to extract the parameters passed into a function from the arguments object.

The args variable is a real array. It has a copy of all the parameters passed to the transitionTo function. From this example, we learn that a quick way to get all the arguments as an array passed to a function is to do:. We will discuss how to use the apply method with the arguments array-like object again for variadic functions.

More on this later. Sure, it is just as easy, even recommended, to borrow our own custom methods and functions. You might be wondering what will happen if the original definition of the method we are borrowing changes.

Will the borrowed copied method change as well, or is the copied method a full copy that does not refer back to the original method? As expected, if we change the original method, the changes are reflected in the borrowed instances of that method. This is expected for good reason: Use Apply to Execute Variable-Arity Functions To wrap up our discussion on the versatility and usefulness of the Apply, Call, and Bind methods, we will discuss a neat, little feature of the Apply method: We can pass an array with of arguments to a function and, by virtue of using the apply method, the function will execute the items in the array as if we called the function like this:.

This technique is especially used for creating variable-arityalso known as variadic functions. These are functions that accept any number of arguments instead of a fixed number of arguments. The arity make money tucson az a function specifies the number of arguments the function was defined to accept. This is where the apply method helps us execute variadic functions.

Instead of the above, we have to pass the array of numbers using apply thus:. Here is an example of our own variadic function to further illustrate the concept of using the apply method in this capacity:. The Call, Apply, and Bind methods are indeed workhorses and should be part of your JavaScript repertoire for setting the this value in functions, for creating and executing variadic functions, and for borrowing methods and functions. As a JavaScript developer, you will likely encounter and use these functions time and again.

So be sure you understand them well. Crockford is a complex guy. Later when I have a bit of timeI will expound on his bind method to make it clearer.

javascript - Call function with array of arguments - Stack Overflow

Do you recommend JS: I think it like the book that tech you how to write code like Mr. That is a good book, but not to use as your first book. It should be your second or third book, after you have already learned the basics and understand JavaScript well. Ever since i have stumbled upon your blog, i must say that my JS concepts have improved a lot. You have unique ability to simplify things in such a way it is easy to grasp. Keep up the good work.

May be someday you should author a book. Another well explained JS concept.

The OOP in JavaScript post was published in JavaScript Weekly. That was the only one, so I know what you mean. I learn something new every time i visit your blog. Thank you, Ritesh, and you are welcome. Hi Richard, I really love reading your articles and appreciate your work in here; even simple examples guide n00bies very well.

Thank you and wish to see more of them. Emre, your suggestion that falsy will be the result from a nonexistent or empty parameter is correct. Here is a working example on JSbin: Oops i missed that, my mistake. Could you please provide example using Microsoft Visual Basic 6. I think VB6 is more performant and powerful than the Java scripting language. Ye, borrow is the key. Hi Richard, I find a tricky part when borrow method, I modify the code as following: Since gameController does NOT have avsScore property, but it still works and get the result stock market crash of 1929 over speculation As a note, I was working through most of the examples using the REPL available to Node v.

Thanks for binary search tree functions c the time to share this with the rest of the readers. It is very helpful. I take it you are referring to this function:. I am not sure why the code example had analisis tecnico forex tiempo real error with REPL.

What happens if you add the return statement after the line: Thanks for the javascript call function with arguments I realized that my interpretation of the intent of that code example was incorrect. Originally, I thought that the avg function was to immediately return the average value of a given array if say calling console.

So on my part, it was actually me with the code hiccup, haha! Your articles are helpful and well explained. But could I please ask you to remove any bucharest stock exchange trading calendar spaces from the lines in your code samples?

Your layout is so narrow that the extra spaces at the beginning csv forex historical data each line make nearly every line of code wrap.

It makes it harder to read your code. Hi Javascript call function with arguments, love this website! I came up with the following, but wanted to double check that I had conceptualized it right:. Can you please explain following concept: You correctly note that this is bad practice, because the cars object might already have a showData method that we would be accidentally overwriting.

In which case, is there even a problem using bind to borrow? Is the code for found correct? Thank you for the explanation on borrowing methods. I just tried it in one of my scripts and it works great. It saved me from a tedious workaround. This stock broker malaysia vacancy is just what I was looking for.

There is btw not a single YouTube video which adequately explains this subject hint hint …. I understand how this example works. Wonderful blog post; thank you writing it! I have a question about the example given for currying function with the bind method.

JavaScript Arguments Object Function Tutorial

In the function below, the arguments are listed in the order: How does the JS interpreter know that when the function is called, the argument given corresponds to the name parameter and is not overwriting the first argument gender? You are right that the following code creates or potentially overwrites a showData method on cars… cars. However, you can easily use bind to borrow the showData method from users without creating it on cars by immediately calling it… user. Would be even better if you could explain the fundamental differences between bind, call and apply though.

This is the best site for javascript learning. Objects behaving like an array — Man! Till yesterday, I thought arguments object can access only length property, but not anymore.

I am indulging this newly acquired knowledge. Almost all tutorial on apply and call seemed a little difficult to me. But, this article made everything easy for me to understand. The examples were really helpful and things were generally just written in a clear, concise way.

Can you please update your article and add one missing bit: For this example, since gameController. Thanks for awesome article. I have one question. Thank you for such a wonderfully simple explanations of js concepts! I am active js developer with almost 2 years of ex. Am preparing for work interview and thought I should sort some things out in my head.

Your blog has REALLY helped me to do all that. Thanks a ton Richard! Thanks Richard for wonderful article. Now, I could feel better with javascript. I have a doubt on function currying example. Below is my code snippet. Question is in comment. This works fine for me although i did not use bind to set this. How come passing 1 as argument is setting this object. I always search for sites to recycle my knowledge and I must say that yours is one of the best I found.

Really helped me to remember and even learn new stuffs. Thanks for wonderful articleI cannot think of learning javascript through any other medium. I have one doubt in call example given above illustrating how to set this to point to particular objectwe have reset global variable: I learnt a lot from your post Richard, thank you very much for being awesome and sharing your knowledge to the world like you do!

Now I can continue learning more about functional programming in Javasript. I really loved it, dude. Well explained articles, with a lot of advanced stuff that I really did not understand at all, now I can. Thanks and keep doing this great job. I will take you advice and update the article accordingly, when time permits. Leave this field empty. Notify me of follow-up comments by email.

Notify me of new posts by email. Invest in Your Future: Advanced JavaScriptApplyBindCallIntermediate JavascriptLearn JavaScript Richard Thanks for your time; please come back soon.

July 15, at 1: The bind from douglas crockford example is really hard to understand. July 17, at 3: July 18, at 1: July 31, at July 17, at You are awesome as usual! Thanks for your time! Thank you for reading the blog, and you are welcome. July 17, at 5: July 30, at 9: July 18, at 2: July 23, at 1: July 31, at 1: Sri, you are wonderful.

Thanks for the wonderful words of encouragement. July 25, at July 31, at 2: August 6, at 2: August 6, at 8: August 6, at 9: August 19, at 5: August 19, at 8: August 23, at 5: August 23, at You are very welcome, Yougen. I am glad this article was helpful for you. September 27, at Currying is not the same thing as partial function application.

Richard Of Stanley Author. October 1, at 2: October 1, at 3: October 14, at 7: Similar post can be found here http: October 16, at 6: Please keep up the great work on your blog! October 23, at 3: HI Watertype, Thanks for taking the time to share this with the rest of the readers. I take it you are referring to this function: October 23, at 4: Hello again Richard, Thanks for the reply! You are welcome, and thanks for following up.

December 11, at January 7, at March 4, at 8: I am confused about why the apply and call methods might be needed for getting the arguments. April 3, at 1: I came up with the following, but wanted to double check that I had conceptualized it right: April 9, at April 24, at 4: September 8, at 7: Another thanks for these useful collection of posts. November 3, at November 9, at 7: November 18, at 7: I apologise in advance for my weak english.

November 23, at 8: December 4, at 8: January 5, at Thanks for the great post! I have a question on your illustration: January 29, at February 9, at 9: February 23, at 8: March 7, at March 10, at 2: I have learn a lot from your posts.

March 17, at 6: March 28, at 2: April 30, at May 6, at Thank You so much for the great articles. May 27, at 8: June 11, at 6: July 20, at September 11, at 3: September 26, at 2: October 2, at October 16, at 4: Thank You so much for the great articles and time. October 19, at 2: October 26, at 6: November 1, at 9: November 12, at 2: What a great article. I really appreciate it and it helped clear up a lot of issues for me! November 13, at 2: Is the below a mistake? November 25, at 9: January 31, at 4: February 10, at 7: February 12, at Now, I could feel better with javascript I have a doubt on function currying example.

March 13, at 9: April 19, at 2: Hi RichardThanks for wonderful articleI cannot think of learning javascript through any other medium I have one doubt in call example given above illustrating how to set this to point to particular objectwe have reset global variable: April 25, at 8: May 6, at 6: October 6, at November 10, at 2: Thanks for your comment, Leah.

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