Array Functions 相关源码拾遗 & 小结

[lessfish]

Array Functions 相关源码拾遗 & 小结

[WangBoxue]

仔细一想，如果已经实现了 _.difference，我们把 _.without 的参数放入数组，然后传入 _.difference 就 ok 了！倒过来就不行了（思考下为什么）。

感觉倒过来也可以

var args = _.union(arg1, arg2, ...);
args.unshift(array);
_.without.apply(null, args);

我哪里错了吗？

[lessfish]

_.without.apply(null, args);

这步的结果还是 args 吧？不知道我有没有理解错 @WangBoxue

[WangBoxue]

@hanzichi
https://jsfiddle.net/WangBoxue/1z03b4h4/

apply() 方法在指定 this 值和参数（参数以数组或类数组对象的形式存在）的情况下调用某个函数。
所以执行_.without.apply(null, args)相当于_.without(array, elements in arg1, elements in arg2, ...)

[lessfish]

@WangBoxue 的确如此，感谢指出！

[aleen42]

@WangBoxue @hanzichi

反过来实现可能需要通知 _.without() 是否是 _.difference() 来调用它。如果是，则展开参数中的所有数组，不然则不展开。当然，前提是 _.difference() 要保证调用 _.without() 时没有传递非数组元素。

_.without = function(array) {
    var rest = (this == 'difference') ? _.flatten(arguments, false, false, 1) : Array.prototype.slice.call(arugments, 1);
    
    return _.filter(array, function(value) {
        return !_.contains(rest, value);
    });
};

_.difference = function(array) {
    /** filter out arguments which is not an array firstly */
    var args = _.flatten(arguments, true, true, 1).unshift(array);

    /**
     * let the method `_.without()` know that whether it's called by `_.difference()`,
     * if so, then flatten all the arrays from argments,
     * if not, then do not flatten.
     */
    return _.without.apply('difference', args);
};

[shaunzeng]

hey I have another question if you dont mind?

So in _.sample function, what is the point of having a Math.max(0,n) passed in _.shuffle function, instead of passing just 'n' ? also why does it check for object before using shuffle? because shuffle function already checks for objects? it that redundant ? please let me know what you think?

[shaunzeng]

also, why does _.map function use cb(iteratee, context), instead of optimizeCb(iteratee, context) ? you cannot pass anything else but a function in _.map right? so it should be optimizeCb I think, i tried to pass other stuff but it kind of broke the _.map code. Please let me kow what you think? thanks a ton!

[WangNianyi2001]

@shaunzeng Math.max 是过滤负数= =