A collection of useful prototypes that I use.

prototypes.js

/**
 * First letter of a string converted into uppercase
 */
String.prototype.capitalizeFirstLetter = function () {
    return this
        .charAt(0)
        .toUpperCase() + this.slice(1);
}

/**
 * ES6 template strings in ES5
 */
String.prototype.eval = function (data) {
    return this.replace(/\${(.*?)}/g, function (_, code) {
        var scoped = code.replace(/(["'\.\w\$]+)/g, function (match) {
            return /["']/.test(match[0])
                ? match
                : 'scope.' + match
        });
        try {
            return new Function('scope', 'return ' + scoped)(data)
        } catch (e) {
            return ''
        }
    })
}

/**
 * Add a number to all the elements
 */
Array.prototype.addToAll = function (adder) {
    return this.map(function (x) {
        return x + adder;
    });
}

/**
 * Slugify the string
 */
String.prototype.slugify = function () {
    return this
        .toString()
        .toLowerCase()
        .replace(/\s+/g, '-')
        .replace(/[^\w\-]+/g, '')   // Remove all non-word chars
        .replace(/\-\-+/g, '-')     // Replace multiple - with single -
        .replace(/^-+/, '')         // Trim - from start of text
        .replace(/-+$/, '');        // Trim - from end of text
}