ECMAscript variable scope summary tutorial

This article mainly introduces the ECMAscript variable scope, and explains it through two scenarios: using the var operator declaration and not using the var operator declaration. You can check the detailed explanation below for the specific operation steps. Interested readers Partners can refer to it.

The difference between variables declared using the var operator and variables declared without the var operator

Javascript is a product that follows the ECMAScript standard , Naturally, ECMAScript standards must be followed

ECMAScript variables are loosely typed, that is, they can be used to save any type of data (uninitialized variables will save a special value of undefined).

Not declared using the var operator

  function test() {
    message='hi';
    console.log(message);
  }
  console.log(message);

The variable message not declared using the var operator is global Variable, if the test() method is not called, the message is in an undefined state.

function test() {
    message='hi';
    console.log(message);
  }
  test();
  console.log(message);

The variable message that is not declared using the var operator is a global variable and the test() method must be called. will be effective.

Use the var operator to declare

local variables

function test() {
    var message='hi';
    console.log(message);
  }
  test(); 
  console.log(message);

For variables declared with var within a function, the message is destroyed after calling the test() method, and the console output cannot find this variable.

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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