数字的千分位格式化方法

方法一：数组（字串）循环法

function toThousands(num) {
    var result = [ ], counter = 0;
    num = (num || 0).toString().split('');
    for (var i = num.length - 1; i >= 0; i--) {
        counter++;
        result.unshift(num[i]);
        if (!(counter % 3) && i != 0) { 
                result.unshift(','); 
        }
    }
    return result.join('');
}

function toThousands(num) {
    var result = '', counter = 0;
    num = (num || 0).toString();
    for (var i = num.length - 1; i >= 0; i--) {
        counter++;
        result = num.charAt(i) + result;
        if (!(counter % 3) && i != 0) { 
                result = ',' + result; 
        }
    }
    return result;
}

方法二：字串截取法

function toThousands(num) {
    var num = (num || 0).toString(), result = '';
    while (num.length > 3) {
        result = ',' + num.slice(-3) + result;
        num = num.slice(0, num.length - 3);
    }
    if (num) {
        result = num + result; 
    }
    return result;
}

方法三：正则表达式法

function toThousands(num) {
    return (num || 0).toString().replace(/(d)(?=(?:d{3})+$)/g, '$1,');
}

方法四：转换格式法

function toThousands(num) {
    return (num || 0).toLocaleString('en-US');
}