Javascript 字符串填充

2019-11-12

在 JavaScript 中字符串填充可以使用 String.prototype.padStart() 和 String.prototype.padEnd()

以 padStart() 为例，效果如下

'abc'.padStart(10);         // "       abc"
'abc'.padStart(10, "foo");  // "foofoofabc"
'abc'.padStart(6,"123465"); // "123abc"
'abc'.padStart(8, "0");     // "00000abc"
'abc'.padStart(1);          // "abc"

在浏览器的支持版本如下

对于不知道的版本，我们可以自己加上这个方法，在代码运行前执行如下代码即可。

// https://github.com/uxitten/polyfill/blob/master/string.polyfill.js
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart
if (!String.prototype.padStart) {
    String.prototype.padStart = function padStart(targetLength, padString) {
        targetLength = targetLength >> 0; //truncate if number, or convert non-number to 0;
        padString = String(typeof padString !== 'undefined' ? padString : ' ');
        if (this.length >= targetLength) {
            return String(this);
        } else {
            targetLength = targetLength - this.length;
            if (targetLength > padString.length) {
                padString += padString.repeat(targetLength / padString.length); //append to original to ensure we are longer than needed
            }
            return padString.slice(0, targetLength) + String(this);
        }
    };
}

padEnd() 的代码如下

// https://github.com/uxitten/polyfill/blob/master/string.polyfill.js
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padEnd
if (!String.prototype.padEnd) {
    String.prototype.padEnd = function padEnd(targetLength,padString) {
        targetLength = targetLength>>0; //floor if number or convert non-number to 0;
        padString = String((typeof padString !== 'undefined' ? padString : ' '));
        if (this.length > targetLength) {
            return String(this);
        }
        else {
            targetLength = targetLength-this.length;
            if (targetLength > padString.length) {
                padString += padString.repeat(targetLength/padString.length); //append to original to ensure we are longer than needed
            }
            return String(this) + padString.slice(0,targetLength);
        }
    };
}

String.prototype.padStart()