Pass function as parameter JavaScript | Example code

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JavaScript Functions is ‘first class’ and treated like any other variable. When the function is passed as a parameter to another function, they’re known as a ‘callback’ in JavaScript. That is called when the other function is ready for them.

Example Pass function as parameter JavaScript

Simple example code. If you want to pass a function, just reference it by name without the parentheses:

  <html>
  <head>


    <script type="text/javascript">

      function foo(x) {
        alert(x);
      }

      function bar(func) {
        func("Hello World!");
      }

      //alerts "Hello World!"
      bar(foo);
</script>
</head>

</html>

Output:

Pass function as parameter JavaScript

But sometimes you might want to pass a function with arguments included, but not have it called until the callback is invoked. To do this, when calling it, just wrap it in an anonymous function, like this:

function foo(x) {
   alert(x);
}
function bar(func) {
   func();
}

//alerts "Hello World!" (from within bar AFTER being passed)
bar(function(){ foo("Hello World!") });

If you prefer, you could also use the apply function and have a third parameter that is an array of the arguments, like such:

function eat(food1, food2)
{
    alert("I like to eat " + food1 + " and " + food2 );
}
function myFunc(callback, args)
{
    //do stuff
    //...
    //execute callback when finished
    callback.apply(this, args);
}

//alerts "I like to eat pickles and peanut butter"
myFunc(eat, ["pickles", "peanut butter"]); 

Source: https://stackoverflow.com

Do comment if you have any doubts or suggestions on this JS function topic.

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.

OS: Windows 10

Code: HTML 5 Version

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