Both ES5 and ES6 are versions of the JavaScript language. ES5 was released in 2009, and ES6 was released in 2015. There are the following differences between the two:
1. Different ways of declaring variables: ES5 uses the var keyword to declare variables, while ES6 introduces the let and const keywords to declare variables.
2. Block-level scope: In ES5, there are only global scope and function scope, while ES6 adds block-level scope. For variables declared inside code blocks such as if, for, and switch, they are not external. visible.
3. Arrow functions: Arrow functions are newly added in ES6, which can define functions more concisely. At the same time, arrow functions do not have their own this, and its this is bound to the this of the parent scope.
4. String template: The string template function has been added in ES6, and backticks (`) can be used to define multi-line text and embedded expressions.
5. Classes and inheritance: The class keyword was introduced in ES6 to implement classes and inheritance, making object-oriented programming more convenient.
6. Modularity: The concept of modularity was introduced in ES6, and the export and import of modules are realized through the export and import keywords.
7. Destructuring assignment: ES6 introduces destructuring assignment syntax, which can easily extract values from arrays or objects and assign them to variables.
8. Promise object: The Promise object was introduced in ES6, which can handle asynchronous operations more elegantly.
9. Others: ES6 also adds some new data structures and methods, such as Set, Map, Symbol, etc. At the same time, the default values of function parameters, rest parameters, etc. have also been enhanced and optimized.
In short, ES6 is a more complete and modern version of JavaScript than ES5, providing more convenient syntax and functional features, enabling developers to develop more efficiently and comfortably.