New ES6 features you must know: Detailed explanation of let and const commands

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.

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.

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 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.

Detailed explanation and code examples of const in C In C language, the const keyword is used to define constants, which means that the value of the variable cannot be modified during program execution. The const keyword can be used to modify variables, function parameters, and function return values. This article will provide a detailed analysis of the use of the const keyword in C language and provide specific code examples. const modified variable When const is used to modify a variable, it means that the variable is a read-only variable and cannot be modified once it is assigned a value. For example: constint

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.