What are the JS skills?

This article mainly explains "what are the JS skills". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn what JS skills are there.

1. Ternary operator

green hand

Let hungry = true; let eat; if (hungry = = true) {eat = 'yes';} else {eat =' no';}

Veteran

Let hungry = true; let eat = hungry = = true? 'yes': 'no'

two。 Digit to string / string to digit

green hand

Let num = 15; let s = num.toString (); / / number to string let n = Number (s); / / string to number

Veteran

Let num = 15; let s = num + ""; / / digit to string let n = + s; / / string to digit

3. Fill array

green hand

For (let item0; I

< arraySize; i++){ filledArray[i] {'hello' : 'goodbye'}; } 老手 let filledArray = new Array(arraysize).fill(null).map(()=>

({'hello':' goodbye'}))

4. Dynamic properties of an object

green hand

Let dynamic = "value"; let user = {id: 1,}; user [dynamic] = "other value"

Veteran

Let dynamic = "value"; let user = {id: 1, [dynamic] = "other value"}

5. Delete duplicates

green hand

Let array = [100,23,23,23,23,67,45]; let outputArray = []; let flag = false; for (j = 0)

< array.length; j++) { for (k = 0; k < outputArray.length; k++) { if (array[j] == outputArray[k]) { flag = true; } } if (flag == false) { outputArray.push(array[j]); } flag = false; } // tArray = [100, 23, 67, 45] 老手 let array = [100, 23, 23, 23, 23, 67, 45]; let outputArray = Array.from(new Set(array)) 6. 数组到对象 新手 et arr = ["value1", "value2", "value3"]; let arrObject = {}; for (let i = 0; i < arr.length; ++i) { if (arr[i] !== undefined) { arrObject[i] = arr[i]; } } 老手 let arr = ["value1", "value2", "value3"]; let arrObject = {...arr}; 7.对象到数组 新手 let number = { one: 1, two: 2, }; let keys = []; for (let numbers in numbers) { if (number.hasOwnProperty(number)) { keys.push(number); } } // key = [ 'one', 'two' ] 老手 let number = { one: 1, two: 2, }; let key = Object.keys(numbers); // key = [ 'one', 'two' ] let value = Object.values(numbers); // value = [ 1, 2 ] let entry = Object.entries(numbers); // entry = [['one' : 1], ['two' : 2]] 8. 短路条件 新手 if (docs) { goToDocs(); } 老手 docs && goToDocs() 9. 使用^检查数字是否相等 if(a!=123) // before // 一般开发者 if(a^123) // after // B格比较高的 10.对象遍历 const age = { Rahul: 20, max: 16 }; // 方案1：先得 key 在便利 key const keys = Object.keys(age); keys.forEach(key =>

Age [key] +); console.log (age); / / {Rahul: 21, max: 16} / / solution 2-`for.in` cyclic for (let key in age) {age [key] +;} console.log (age); / / {Rahul: 22, max: 18}

11. Get all the keys of the object

Cosnt obj = {name: "Front-end Intelligence", age: 16, address: "Xiamen", profession: "Front-end Development",}; console.log (Object.keys (obj)); / / name, age, address, profession

twelve。 Check whether the value is an array

Const arr = [1,2,3]; console.log (typeof arr); / / object console.log (Array.isArray (arr)); / / true

13. Initialize an array of size n and fill in the default values

Const size = 5; const defaultValue = 0; const arr = Array (size) .fill (defaultValue); console.log (arr); / / [0,0,0,0,0]

14. True value and imaginary value

Imaginary values: false,0, "", null,undefined and NaN.

Truth: "Values", 0 ", {}, [].

15. The difference between third-class sign and double-equal sign

/ / A pair of equal signs-converts two operands to the same type, and then compares console.log (0 = ='o'); / / true / / third class sign-does not convert to the same type console.log (0 = ='0'); / / false

16. A better way to receive parameters

Function downloadData (url, resourceId, searchTest, pageNo, limit) {} downloadData (...); / / need to remember the order

A simpler way

Function downloadData ({url, resourceId, searchTest, pageNo, limit} = {}) {} downloadData ({resourceId: 2, url: "/ posts", searchText: "WebDev"})

17.null vs undefined

Null = > it is a value, but undefined is not.

Const fn = (x = 'default value') = > console.log (x); fn (undefined); / / default value fn (); / / default value fn (null); / / null

When passing null, the default value is not used, and when undefined or nothing is passed, the default value is used.

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