A utility function to extract convenient multi-line strings with embedded variables from comments in function bodies. Particularly useful for inline GLSL shader code.

textFromComment.js

/**
 * Extract a multiline string from a multiline comment inside a function.
 *
 * @param {Function} fn The function containing the string.
 * @param {vars} A map of tokens to values to replace in the string.
 */
function textFromComment(fn, vars) {
    var s = (fn + '').match(/^[\s\S]*?\/\*!?\s*([\s\S]+?)\s*\*\/$/m)[1];
    if (typeof vars !== 'undefined') {
        var keys = Object.keys(vars).sort(function(a, b) { return b.length - a.length; });
        for (var i = 0, l = keys.length; i < l; i++) {
            var key = keys[i], val = vars[key];
            s = s.split('$' + key).join(val);
        }
    }
    return s;
}

/* Usage example */
textFromComment(fragmentShader, {
    assignTextures: assign,
    declareTextures: declare,
});
function fragmentShader() {
    /*!
    varying vec2 vUv;
    varying vec3 vPosition;
$declareTextures
    void main() {
        vec4 color = texture2D( texture_0, vUv ); // base
$assignTextures
        gl_FragColor = color;
    }
    */
    var z; // prevent UglifyJS from removing the above comment
}