类数组、可遍历 对象(arguments selector返回的对象)转成数组
let arrayLike = {
'0': 'a',
'1': 'b',
'2': 'c',
'3': 'd',
length: 4
};
Array.from()
let arr1 = Array.from(arrayLike); // ['a', 'b', 'c']
Array.from()
var arr2 = Array.from([1, 2, 3], (x)=>x*x) // [1,4,9]
// 等同于Array.from(arrayLike).map(x => x * x);
Array.of()
var arr3 = Array.of(3, 11, 8) // [3,11,8]
var arr4 = Array.of(3) // [3]
var arr5 = Array.of(3).length // 1
Array.copyWithin()
// [].copyWithin() 1是截取段的起始位置,4-6是截取区间
var arr6 = [33, 44, 55, 66, 77, 88].copyWithin(1, 4, 6) //[33,77,88,66,77,88],会改变原数组
Array.find()
var arr7 = [1, 5, 10, 15].find(function(value, index, arr) {
return value > 9;
}) // 10,没有就返回underfined
Array.findIndex()
var arr8 = [1, 5, 10, 15].findIndex(function(value, index, arr) {
return value > 119;
}) // 2,没有就返回-1
var index = [NaN].findIndex(y => Object.is(NaN, y)) //0
遍历keys values entries
for( let index of ["L", "X", "D", "Y"].keys()){
//console.log( index )
}
for( let value of ["L", "X", "D", "Y"].values()){
//console.log( value )
}
for( let [index, value] of ["L", "X", "D", "Y"].entries()){
//console.log( index +" : "+value )
}
array.includes()
//array.includes(),第二个参数表示起始位置
[1, 2, 3].includes(2); // true
[1, 2, 3].includes(4); // false
[1, 2, NaN].includes(NaN); // true
[1, 2, 3].includes(3, 3); // false
[1, 2, 3].includes(3, -1); // true
array.forEach()
// forEach方法
[,'z'].forEach((x,i) => console.log(x)); // z
array.filter
// filter方法
var arr10 = ['a',,'b'].filter(x => true) // ['a','b']
console.log(arr10)
array.every
// every方法
var arr11 = [,'a'].every(x => x==='a') // true
console.log(arr11)
array.some
// some方法
var arr12 = [,'a'].some(x => x !== 'a') // false
console.log(arr12)
array.map
// map方法
var arr13 = [,'a'].map(x => 1) // [,1]
console.log(arr13)
array.join
// join方法
var arr14 = [,'a',undefined,null].join('#') // "#a##"
console.log(arr14)
array.toString
// toString方法
var arr15 = [,'a',undefined,null].toString() // ",a,,"
console.log(arr15)
