JavaScript遍历数组的方法详解

var arr = ['a','b','c','d'];

"use strict";var arr = [&#39;a&#39;,&#39;b&#39;,&#39;c&#39;,&#39;d&#39;];var arrUp = [];for(var i = 0; i < arr.length; i++){
    arrUp.push(arr[i].toUpperCase());
}
console.log(arrUp);             //['A','B','C','D']

"use strict";var arr = ['a','b','c','d'];var arrUp = [];for(var i in arr){
    arrUp.push(arr[i].toUpperCase());
}
console.log(arrUp);             //['A','B','C','D']

"use strict";var arr = ['a','b','c','d'];var arrUp = [];
arr.forEach(function(key, index, array){
    arrUp.push(key.toUpperCase());
});
console.log(arrUp);             //['A','B','C','D']

"use strict";var arr = ['a','b','c','d'];var arrUp = arr.map(function(key, index, array){
    return key.toUpperCase();
});
console.log(arrUp);             //['A','B','C','D']

var arr = [1, 4, 10, 5, 8];

//要接受的函数，本文叫判断函数function(key, index, array){
    //key： 数组项值
    //index： 该项的数组下标
    //arr：待操作的数组}

"use strict";var arr = [1, 4, 10, 5, 8];var arrTest = arr.every(function(key, index, array){
    return (key > 2);
});
console.log(arrTest);   //false

"use strict";var arr = [1, 4, 10, 5, 8];var arrTest = arr.filter(function(key, index, array){
    return (key > 6);
});
console.log(arrTest);   //[10, 8]

"use strict";var arr = [1, 4, 10, 5, 8];var arrTest = arr.some(function(key, index, array){
    return (key > 6);
});
console.log(arrTest);   //true