您可以将自己的原型制作splice()为String。

Polyfill

if (!String.prototype.splice) {
    /**
     * {JSDoc}
     *
     * The splice() method changes the content of a string by removing a range of
     * characters and/or adding new characters.
     *
     * @this {String}
     * @param {number} start Index at which to start changing the string.
     * @param {number} delCount An integer indicating the number of old chars to remove.
     * @param {string} newSubStr The String that is spliced in.
     * @return {string} A new string with the spliced substring.
     */
    String.prototype.splice = function(start, delCount, newSubStr) {
        return this.slice(0, start) + newSubStr + this.slice(start + Math.abs(delCount));
    };
}

例

String.prototype.splice = function(idx, rem, str) {

    return this.slice(0, idx) + str + this.slice(idx + Math.abs(rem));

};



var result = "foo baz".splice(4, 0, "bar ");



document.body.innerHTML = result; // "foo bar baz"

编辑： 对其进行了修改，以确保它rem是一个绝对值。