call、apply手写实现与应用

call

Function.prototype.myCall = function () {
    var ctx = arguments[0] || window;
    ctx.fn = this;
    var args = [];
    for (var i = 1; i < arguments.length; i++) {
        args.push('arguments[' + i + ']');
    }
    var result = eval('ctx.fn(' + args.join(',') + ')');
    delete ctx.fn;
    return result;
}

apply

Function.prototype.myApply = function(ctx, arr) {
    var ctx = ctx || window;
    ctx.fn = this;
    var result;
    if (!arr) {
       result = ctx.fn();
       delete ctx.fn;
       return result;
    } else {
        var args = [];
        for (var i = 0; i < arr.length; i++) {
            args.push('arr[' + i + ']');
        }
        result = eval('ctx.fn(' + args.join(',') + ')');
        delete ctx.fn;
        return result;
    }
}