ES6 new method

ES6 The new method

includes()

Format ：arr.includes( Find value , Where to start searching )

// Find the corresponding value and return true, Otherwise return to false
'abc'.includes('a')

padStart() and padEnd()

Format ：str.padStart( The total number of digits in the string , Add the corresponding string )/padEnd( The total number of digits in the string , Add string )

// Once upon a time, I began to complete the string 
'x'.padStart(5,'ab')  //ababx
// Complete the string from after 
'x'.padEnd(5,'ab')  //xabab

Be careful ：

1. The length of the original string is equal to or greater than the maximum length , The original string will not be subtracted , String completion does not take effect , Returns the original string ;
2. The sum of the length of the complement string and the original string exceeds the maximum length , Truncate the complement string exceeding the number of digits , The original string does not move ;
3. If you omit the second parameter , By default, space is used to complete the length

trimStart()/trimLeft() And trimEnd()/trimRight()

Format ：str. trimStart()

// Remove the space on the left , No removal in the middle 
' x y'.padStart()/trimLeft()  //x y
// Remove the space on the right , No removal in the middle 
'x '.padEnd()/trimRight()  //x

Array.from()

Format ：Array.from( data , Data manipulation ,this Point to )

// Convert other data types to arrays 
console.log(Array.from('hello')); //['h','e','l','l','o']
// Have length Property 
// Key names can only be indexes 
const obj = {
    
	'0': 'xxx',
	'1': 18,
	length: 2
}
console.log(Array.from(obj))

console.log(Array.from('12', (value)=>value*2) //[2,4]

find()

Format ：arr.find(function(value, index, arr){},this Point to )

// Find a value that meets the criteria and return immediately 
[1,2,3,4].find((value)=>value>2)

findIndex()

Format ：arr.findIndex(function(value, index, arr){},this Point to )

// Find a value that matches the criteria , Return the index of this value to 
[1,2,3,4].findIndex((value)=>value>2)

Object.assign()

Format ：Object.assign(obj1, obj2)

// Merge objects , Merge directly into the first parameter , Returns the merged object 
const obj1 = {
    
	name: 'xxx',
	age: 18
}
const obj2 = {
    
	name: 'yyy',
	age: 18,
	sex: 'male'
}
Object.assign(obj1, obj2); //{name:'yyy', age: 18, sex: 'male'}

Object.keys()、Object.values() And Object.entries()

const obj = {
    
    username: 'yyy',
    age: 18,
    sex: 'female'
}
console.log(Object.keys(obj2));  //['username', 'age', 'sex']

Object The difference between the three methods and the three methods of array ： Array of keys、values、entries It's an instance method , All of them iterator; Object's keys、values、entries Is a constructor method , It's an array