What is strict mode in JavaScript? What are the application scenarios?

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⭐ Column introduction

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⭐ Strict Mode:

Strict mode is a mode of JavaScript that can be used to identify and fix potential errors in some JavaScript code, and make the code more secure and efficient. To enable strict mode, you just need to add the following statement at the beginning of your script:

"use strict";

Or enable strict mode inside the function:

function strictFunction() {
    
    
  "use strict";
  // 严格模式下的代码
}

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⭐ Usage scenarios

Strict mode is particularly useful in the following situations:

1. Error detection: Strict mode will detect some potential errors and throw exceptions. For example, in non-strict mode you can accidentally create a global variable, while in strict mode an error will be thrown if the variable is not used var, letor constdeclared.

   "use strict";
   
   // 错误：未声明的变量
   x = 10;
   

2. Disabled use of reserved words: In strict mode, some reserved words added in ECMAScript 5 are disabled to avoid conflicts with future versions of JavaScript.

   "use strict";
   
   // 错误：使用了保留字
   var let = 10;
   

3. Remove disallowed properties: In strict mode, removing non-configurable properties or undefined variables will throw an error.

   "use strict";
   
   var obj = {
         
         };
   Object.defineProperty(obj, "x", {
         
          configurable: false });
   
   // 错误：删除不可配置的属性
   delete obj.x;
   

4. Handling of this:this Use pointer in the global scope , and also point to when undefinedit is not bound inside the function , which helps avoid unnecessary side effects.thisundefined

   "use strict";
   
   function strictFunction() {
         
         
     console.log(this); // 输出：undefined
   }
   
   strictFunction();
   

5. Disallow octal literals: Octal literals are not allowed in strict mode.

   "use strict";
   
   var num = 010; // 错误：八进制字面量不允许
   

6. Duplicate parameter and attribute names are prohibited: Duplicate parameter or attribute names are not allowed in function parameters and object literals.

   "use strict";
   
   function duplicateParam(a, a) {
         
         
     // 错误：重复的参数名
   }
   
   var obj = {
         
          prop: 1, prop: 2 };
   // 错误：重复的属性名
   

Strict mode helps write more robust and maintainable JavaScript code, and it is recommended to enable it in new projects to help catch potential problems and errors.

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⭐Write at the end

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