What languages do es5 and es6 belong to?
es5 and es6 belong to JavaScript language. JavaScript is a high-level scripting language for the Internet, consisting of three parts: ECMAScript, DOM and BOM; es5 and es6 are two versions of ECMAScript, used to provide the syntax, types, basic objects, etc. of the JS language.
The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.
es5 and es6 belong to JavaScript language.
JavaScript ("JS" for short) is a lightweight object-oriented programming language that can be used in the browser to control page interaction, and can also be used on the server side as the website backend ( With Node.js), JavaScript is a full-stack programming language.
JavaScript is a high-level scripting language that belongs to the Internet. It has been widely used in Web application development. It is often used to add various dynamic functions to web pages and provide users with smoother and more beautiful browsing effects. Usually JavaScript scripts realize their functions by embedding them in HTML.
JavaScript consists of three core parts: ECMAScript, DOM (Document Object Model), and BOM (Browser Object Model).
Core (ECMAScript): The core part of the language, describing the syntax and basic objects of the language.
Document Object Model (DOM): Web page document operation standard, describing methods and interfaces for processing web page content.
Browser Object Model (BOM): The basis for client and browser window operations, describing the methods and interfaces for interacting with the browser.
ECMAScript
ECMA-262 does not refer to web browsers and stipulates the components of the language, including syntax, type, language, key Words, reserved words, operators, objects.
ECMAScript is a description of the language that specifies all aspects of the standard.
ECMAScript Compatible:
Supports all "types, values, objects, properties, functions, and program syntax and semantics" described by ECMA-262.
Supports Unicode character standards.
Add more "types, values, objects, properties, functions" that are not described in ECMA-262. The new features in West Zhejiang that ECMA-262 talks about mainly refer to this standard. New objects and new properties of objects not specified in .
Supports "Program and Regular Expression Syntax" not defined in ECMA-262. This means that the built-in regular expression syntax can be modified and extended.
ECMAScript (ES) version introduction (version release time)
Time | Version | Description |
---|---|---|
June 1997 | ES1.0 was released | In July of that year, the ECMA262 standard was released |
In June 1998 | ES2.0 was released | This version modification fully complies with the ISO/IEC 16262 international standard. |
December 1999 | ES3.0 was released | became the common standard for JavaScript and received widespread support |
October 2007 | ES4.0 draft was released | Major manufacturers had different opinions and the plan was not passed |
Released ES3.1 and renamed it ECMAScript 5 | Abolished ECMAScript 4.0, so version 4.0 does not exist | |
ES 5.0 officially released | ||
ES5.1 released | This version became the ISO international standard (ISO/IEC 16262:2011) | |
ES6 draft released | ||
ES6 was officially released and renamed "ECMAScript 2015" | TC39 The committee decided to release a version of ECMAScript every year | |
ES7 was released, also known as "ECMAScript 2016" | ||
ES8 was released, also known as "ECMAScript 2017" | ||
ES9 was released, also known as "ECMAScript 2018" | ||
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async is es7. async and await are new additions to ES7 and are solutions for asynchronous operations; async/await can be said to be syntactic sugar for co modules and generator functions, solving js asynchronous code with clearer semantics. As the name suggests, async means "asynchronous". Async is used to declare that a function is asynchronous; there is a strict rule between async and await. Both cannot be separated from each other, and await can only be written in async functions.

In ES6, you can use the reverse() method of the array object to achieve array reversal. This method is used to reverse the order of the elements in the array, putting the last element first and the first element last. The syntax "array.reverse()". The reverse() method will modify the original array. If you do not want to modify it, you need to use it with the expansion operator "...", and the syntax is "[...array].reverse()".

For browser compatibility. As a new specification for JS, ES6 adds a lot of new syntax and API. However, modern browsers do not have high support for the new features of ES6, so ES6 code needs to be converted to ES5 code. In the WeChat web developer tools, babel is used by default to convert the developer's ES6 syntax code into ES5 code that is well supported by all three terminals, helping developers solve development problems caused by different environments; only in the project Just configure and check the "ES6 to ES5" option.

Steps: 1. Convert the two arrays to set types respectively, with the syntax "newA=new Set(a);newB=new Set(b);"; 2. Use has() and filter() to find the difference set, with the syntax " new Set([...newA].filter(x =>!newB.has(x)))", the difference set elements will be included in a set collection and returned; 3. Use Array.from to convert the set into an array Type, syntax "Array.from(collection)".

In es5, you can use the for statement and indexOf() function to achieve array deduplication. The syntax "for(i=0;i<array length;i++){a=newArr.indexOf(arr[i]);if(a== -1){...}}". In es6, you can use the spread operator, Array.from() and Set to remove duplication; you need to first convert the array into a Set object to remove duplication, and then use the spread operator or the Array.from() function to convert the Set object back to an array. Just group.

In es6, the temporary dead zone is a syntax error, which refers to the let and const commands that make the block form a closed scope. Within a code block, before a variable is declared using the let/const command, the variable is unavailable and belongs to the variable's "dead zone" before the variable is declared; this is syntactically called a "temporary dead zone". ES6 stipulates that variable promotion does not occur in temporary dead zones and let and const statements, mainly to reduce runtime errors and prevent the variable from being used before it is declared, resulting in unexpected behavior.

No, require is the modular syntax of the CommonJS specification; and the modular syntax of the es6 specification is import. require is loaded at runtime, and import is loaded at compile time; require can be written anywhere in the code, import can only be written at the top of the file and cannot be used in conditional statements or function scopes; module attributes are introduced only when require is run. Therefore, the performance is relatively low. The properties of the module introduced during import compilation have slightly higher performance.

In ES6, you can use the length attribute of the array object to determine how many items there are in the array, that is, to get the number of elements in the array; this attribute can return the number of elements in the array, just use the "array.length" statement. Returns a value representing the number of elements of the array object, that is, the length value.
