Array的一些方法

let arr1 = [1,2,3];
let arr2 = [4,5,6];

console.log(arr1.concat(arr2)); // [1,2,3,4,5,6]
console.log(arr1.concat(4,5)) // [1,2,3,4,5] 
console.log(arr1); // [1,2,3]

let arr = [1,2,3];
console.log(arr.join(‘|‘)); // 1|2|3
console.log(typeof arr.join(‘|‘)); // string
console.log(arr); // [1,2,3]

let arr = [1,2,3];
console.log(arr.pop()); // 3
console.log(typeof arr.pop()) // number
console.log(arr); // [1,2]

let arr = [1,2,3];
let arr1 = [4,5];
// console.log(arr.push(arr1)); // 4 [1,2,3,[4,5]]
console.log(arr.push(4,5)); // 5 
console.log(arr); // [1,2,3,4,5]

let arr = [1,2,3];
console.log(arr.shift()); // 1
console.log(arr); // [2,3]

let arr = [1,2,3,4];
console.log(arr.unshift(5,6)); // 6
console.log(arr); // [5,6,1,2,3,4]

let arr = [1,4,3,2];
console.log(arr.sort()); // [1,2,3,4]
console.log(arr) // [1,2,3,4]

let arr = [1,4,3,2];
console.log(arr.reverse()); // [2,3,4,1]
console.log(arr); // [2,3,4,1]
console.log(arr.sort().reverse() ) // [4,3,2,1]

let arr = [1,2,3,4];
console.log(arr.slice(0,1)); // [1]
console.log(arr.slice(0,2)); // [1,2]
console.log(arr.slice(1,2)); // [2]
console.log(arr.slice(2,2)); // []
console.log(arr.slice(0,3)); // [1,2,3]
console.log(arr); // [1,2,3,4]

let arr = [1,2,3,4,5];
// console.log(arr.splice(1,1)); // [2]
// console.log(arr); // [1,3,4,5]
// console.log(arr.splice(1,2)); // [2,3]
// console.log(arr.splice(1,2,6)); // [1,6,4,5]
console.log(arr.splice(1,2,...[6,7,8,9])); // [1,6,8,9,4,5]
console.log(arr); // [1,6,8,9,4,5]

 let arr = [‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘]
 arr.map( (c, i) => {
    console.log(i+‘.‘+" "+c)
　　 // 可以return
 })

let arr = [12, 5, 865, 3570];

let result = arr.reduce((temp, item, index) => {
   return temp + item; // temp是每次两个数相加的临时和，第一次是12+5，第二次是17+865，第三次是882+3570
})

console.log(result); // 12+5 +865+3570

let arr = [50, 150, 1800, 2500];

let result = arr.filter( c => c>=1800)

console.log(result);

let arr = [50, 150, 1800, 2500];

arr.forEach( item => {
    console.log(item); 
})