JavaScript中的字符串和数组

var arr = [‘e‘, ‘c‘, ‘r‘, ‘o‘];
var arrnum = [6, 4, 23, 67];

if(arr instanceof Array) {
    console.log(true);
}
if(Array.isArray(arr)) { //ECMAScript 5
    console.log(true);
}

console.log(arr.join(‘,‘));

arr.push(‘x‘);
console.log(arr); //["e", "c", "r", "o", "x"] 
arr.pop();
console.log(arr); //["e", "c", "r", "o"] 

arr.shift();
console.log(arr); //["c", "r", "o"]
arr.unshift(‘d‘);
console.log(arr); //["d", "c", "r", "o"]

console.log(arr.reverse()); //["o", "r", "c", "d"] 
console.log(arr.sort());    //["c", "d", "o", "r"] 
console.log(arrnum.sort()); //转换为字符串后比较 [23, 4, 6, 67] 
console.log(arrnum.sort(compare)); //[4, 6, 23, 67] 
console.log(arrnum.sort(compareEx)); //[4, 6, 23, 67] 

function compare(a, b) {
    if(a < b) {
        return -1;
    } else if(a > b) {
        return 1;
    } else {
        return 0;
    }
}

function compareEx(a, b) {
    return a - b;
}

var arrnew = arr.concat(‘red‘, [‘ss‘, ‘z‘]);
console.log(arrnew); //["e", "c", "r", "o", "red", "ss", "z"] 

console.log(arr.slice(2));      //["r", "o"]
console.log(arr.slice(1, 3));   // ["c", "r"]

//splice 最强大 返回值为删除的组成的数组 自身改变

console.log(arr.splice(1, 3));  //["c", "r", "o"] 
console.log(arr);                    //["e"]

var arr = [‘e‘, ‘c‘, ‘r‘, ‘o‘];   
console.log(arr.splice(2, 0, ‘add‘, ‘dd‘)); //[]
console.log(arr); //["e", "c", "add", "dd", "r", "o"] 

var arr = [‘e‘, ‘c‘, ‘r‘, ‘o‘];
console.log(arr.splice(2, 2, ‘ed‘, ‘fr‘)); //["r", "o"] 
console.log(arr); //["e", "c", "ed", "fr"] 

var arr = [‘e‘, ‘c‘, ‘r‘, ‘o‘];
console.log(arr.indexOf(‘t‘)); //-1
console.log(arr.indexOf(‘c‘)); //1
console.log(arr.lastIndexOf(‘c‘)); //1

var num = [1, 3, 5, 10, 56, 11];
var r = num.every(function(item, index, array) { 
        //所有满足返回true
    return (item % 2 == 0);
});
console.log(r);

r = num.filter(function(item, index, array) {
        //过滤
    return (item % 2 == 0);
});
console.log(r);

r = num.some(function(item, index, array) {
       //一个符合就返回true
    return (item % 2 == 0);
});
console.log(r);

r = num.map(function(item, index, array) {
        //返回新数组
    return (item - 1);
});
console.log(r);

//对每项操作
num.forEach(function(item, index, array) {
    console.log(item);
});

//参数：前一项，当前项，序号，数组

var num = [1, 3, 5, 10, 56, 11];
var sum = num.reduce(function(pre, cur, index, array) {
    return pre + cur;
});
console.log(sum);  //86

var sum = num.reduceRight(function(pre, cur, index, array) {
    console.log(pre + ‘ ‘ + cur);
    return pre - cur;
});
console.log(sum); //-64

var name = ‘zjzhome‘;
console.log(name.charAt(1));  //j

console.log(name.substring(1, 3)); //和slice类似 首选slice //jz
console.log(name.substr(3)); //home
console.log(name.substr(1, 3)); //jzh