Example analysis of JavaScript strict usage

This article describes the usage of JavaScript strict mode. Share it for your reference, as follows:

The purpose of using "use strict" is to specify that the code is executed under strict conditions.

Strict pattern is declared by adding a "use strict"; expression to the head of a script or function.

Undeclared variables are not allowed.

"use strict";
myFunction();
function myFunction() {
  y = 3.14;  // Error (y is not defined)}

Declaring internal to the function is a local scope (using strict patterns only within the function):

x = 3.14;    // No errors reportedmyFunction();
function myFunction() {
  "use strict";
  y = 3.14;  // Error (y is not defined)}

Not allowed to delete variables or objects

"use strict";
var x = 3.14;
delete x;        // Report an error

Function deletion is not allowed.

"use strict";
function x(p1, p2) {}; 
delete x;        // Report an error

Variable duplicate names are not allowed:

"use strict";
function x(p1, p1) {};  // Report an error

Octal is not allowed:

"use strict";
var x = 010;       // Report an error

Escape characters are not allowed:

"use strict";
var x = \010;      // Report an error

Assigning values ​​to read-only attributes is not allowed:

"use strict";
var obj = {};
(obj, "x", {value:0, writable:false});
 = 3.14;      // Report an error

Deletion of an attribute that is not allowed is not allowed:

"use strict";
delete ; // Report an error

The variable name cannot use the "eval" string:

"use strict";
var eval = 3.14;     // Report an error

The variable name cannot use the "arguments" string:

"use strict";
var arguments = 3.14;  // Report an error

Forbid this keyword to point to global objects

Why use strict mode:

• Eliminate some unreasonable and imperfect aspects of Javascript syntax and reduce some weird behaviors;
• Eliminate some insecurities in code operation and ensure the safety of code operation;
• Improve compiler efficiency and increase running speed;
• "Strict Mode" reflects the more reasonable, safer and more rigorous development direction of Javascript. Mainstream browsers including IE 10 have already supported it.

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For more information about JavaScript, you can also view the special topic of this site: "JavaScript object-oriented tutorial》、《Summary of JavaScript Errors and Debugging Skills》、《Summary of JavaScript data structure and algorithm techniques》、《JavaScript traversal algorithm and skills summary"and"Summary of JavaScript mathematical operations usage》

I hope this article will be helpful to everyone's JavaScript programming.