How to use JavaScript functions-JS Tutorial-php.cn

How to use JavaScript functions

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Release： 2018-12-17 13:52:06

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Functions jointly define the same processing and make it available for multiple uses. The following article will introduce you to the usage of functions in How to use How to use JavaScript functions functions.

How to use How to use JavaScript functions functions

If there is a lot of code, sometimes you may need to use a lot of the same processing. Although you can save time by copying and pasting, the code will become very long. , it is inconvenient for some subsequent operations. At this time, we can define the same processing as a function, and then call this function, so that the code will look very concise.

In addition, the function also has an advantage. When part of the code that needs to be processed needs to be changed together, only one place needs to be changed.

Let’s look at the definition of function in How to use How to use JavaScript functions functions

Basic form

The first thing you need when defining a function is function . Then write the name of the function and write the required processing in {}. The simplest way to write it is as follows

<script>
function 函数名( ) {
　　处理的代码
}
</script>

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Parameters and return values

Also, if you want to pass parameters to a function, put the parameter name in parentheses. You can add as many parameters as you need, separated by ",". Therefore, even if the same processing is performed, the content can be processed according to the passed parameters.

In addition, if you want to get the processing result of this calling function, use the return keyword, and the result return value processed in the function will be passed.

<script> 
function 函数名（参数1，参数2，...）{ 
　　处理的代码
　  return 返回值; 
}
</ script>

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Let’s look at

specific examples of using functional programming

We first use variables to write, define the variable as money, according to the value of the input money, use document.write outputs three types of strings: "rich people", "ordinary people", and "poor".

The code is as follows

<!DOCTYPE html>
<html>
  <head>
    <meta charset = "utf-8">
    <title>How to use How to use JavaScript functions functions</title>
  </head>
  <body>
    <script>
      var money;
      if (money > 5000) {
        document.write("有钱人");
      } else if (money > 3000){
        document.write("普通人");
      } else {
        document.write("贫穷");
      }
    </script>
  </body>
</html>

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Based on the above code, according to the input money value, the execution result will be "rich" or "ordinary people" or "poor". If the function is not used, then the same code must be written.

    <script>
      var money=10000;
      if (money > 5000) {
        document.write("有钱人");
      } else if (money > 3000){
        document.write("普通人");
      } else {
        document.write("贫穷");
      }
    </script>

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If the value of variable money is input to 10000, the output result will be "rich man"

How to use How to use JavaScript functions functions

When the variable money input is 4000, the result will be For "ordinary people", when the value of money entered is 2000, it means "poor".

So you only need to change the value of var money, nothing else needs to be changed, but the code will become a lot. At this time, if you define a function, the code will become much simpler

Let’s look at

specific examples of using functions

The function name here is judge. Because I want to judge "rich people", "ordinary people" and "poor people" based on the value of the input variable money.

Actually, you can't tell what information is passed to the function, so the variable money is used to define the parameters. This function will change the output value and string based on the value entered into the variable money.

function judge(money) {
  if (money > 5000) {
    document.write("有钱人");
  } else if (money > 3000){
    document.write("普通人");
  } else {
    document.write("贫穷");
  }
}

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By doing this, you can delete the code that has been written and repeated many times so far and replace it with a function called judge.

The code is as follows

<script>
  function judge(money) {
    if (money > 5000) {
      document.write("有钱人");
    } else if (money > 3000){
      document.write("普通人");
    } else {
      document.write("贫穷");
    }
  }

  var money = 10000;
  judge(money);
  var money = 4000;
  judge(money);
  var money = 2000;
  judge(money);
</script>

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The running result is as follows

How to use JavaScript functions

Use the return value to return

You can also return the string of the judgment result without using document.write. . In this case, use the return value return. After substituting the judgment result strings "rich", "ordinary" and "poor", finally use return to return the value of the result variable.

The code is as follows

<script>
  function judge(money) {
    var result;
    if (money > 5000) {
      result = "有钱人";
    } else if (money > 3000){
      result = "普通人";
    } else {
      result = "贫穷";
    }
      return result;
    }
  var money = 10000;
  var result = judge(money);
  document.write(result);
  var money = 4000;
  var result = judge(money);
  document.write(result);
  var money = 2000;
  var result = judge(money);
  document.write(result);
</script>

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The running effect remains unchanged

How to use JavaScript functions ##Finally, let’s take a brief look

What is local Variables

Local variables refer to variables defined in a function and only have a role in that function.

Using "var variable name" declaration is no different from ordinary variables, but in the case of local variables, it is declared in the function.

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