sliceの原理

Array.prototype.mySlice = function () {
    var start = 0;
    var end = this.length;
    if (arguments.length === 1) {
        start = arguments[0];
    } else if (arguments.length === 2) {
        start = arguments[0];
        end = arguments[1];
    }
    var tmp = [];
    for (var i = start; i < end; i++) {
        tmp.push(this[i]);
    }
    return tmp;
}

var fakeArr = {
    0: 'abc',
    1: 'def',
    2: 'ghi',
    length: 3
}

[].mySlice.call(fakeArr);