How to use JavaScript's immediate execution function-JS Tutorial-php.cn

How to use JavaScript's immediate execution function

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Release： 2018-12-13 17:30:18

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How to use JavaScript’s immediate execution function? This article will introduce to you how to use JavaScript immediate execution functions.

How to use JavaScripts immediate execution function

Let’s take a brief look at what function is?

A function is an event-driven or reusable block of code that executes when it is called.

In other words, if you use a function multiple times, you can simply use it by calling it.

Use fonction, defined as follows.

fonction 函数名(){
执行的代码
}

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Let’s take a look againWhat is an anonymous function?

As the name suggests, an anonymous function is a function whose functionality can be defined without a function name

Using anonymous functions also has the advantage of simplifying the code when using higher-order functions.

A higher-order function is a function that can handle the function itself as a parameter or return value.

In higher-order functions, the function as a parameter is usually used only once, so I can make the code simpler by making it an anonymous function.

Additionally, since you don't need to define a global scope name by making it an anonymous function, you also reduce errors caused by duplicating function names.

Comparison of normal function and anonymous function

Let us compare normal function and anonymous function based on the following program.

function( ) {
 执行的代码
}

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Normal function (named function)

The code is as follows

<!DOCTYPE html>
<html>
  <head>
    <meta charset = "utf-8">
    <title>JavaScript</title>
  </head>
  <body>
    <script>
      function sum(a,b){
        var result = a + b;
        return result;
      }
      var answer = sum(1,2);
      console.log(answer);
    </script>
  </body>
</html>

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When called using console.log, according to parameters 1 and 2 Output "3".

How to use JavaScripts immediate execution function

Anonymous function

Next we use anonymous functions to write the same function

The code is as follows

  <script>
      var sum = function (a,b){
    var result = a + b;
    return result;
  }
  var answer = sum(1,2);
  console.log(answer);
    </script>

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In a named function, we first define the function sum, we later assign sum to the variable answer and call it with parameters 1 and 2.

On the contrary, in an anonymous function, the definition of the function can be entered directly in the variable. Therefore, being able to store the function definition itself in the variable is also an advantage of anonymous functions.

The result is the same

How to use JavaScripts immediate execution function

Finally, let’s take a look at the usage of immediate execution function

immediate function Is an immediately executed function expression, called IIFE (immediately invoked function expression) in English.

The immediate function is executed immediately after it is defined.

Therefore, it is called an immediate execution function.

Use immediate function, as long as the function is defined, it can be executed immediately.

Local variables are declared in a function and used throughout the declared function.

Global variables are variables declared in the global scope, so they can be used anywhere in a JavaScript program.

For example, if a global variable is declared outside a function, it can be used both inside and outside the function.

Let’s look at an example of an immediate function

var declares a variable, and the function definition starting from functions can be executed immediately.

The code is as follows

<script>
    var sum = (function (a,b){
    var result = a + b;
    return result;
  })(1,2);
  console.log(sum);
    </script>

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We execute the function definition by immediately providing parameters to it.

So far we have assigned the function sum to the variable answer and passed the parameters. Omitting it as a variable answer means you can pass arguments directly to the defined function and execute the content.

This program is very smooth since you don't need to use var answer = sum(1,2); to call the function.

The running results are as follows: the result is also 3

How to use JavaScripts immediate execution function

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