Javascript: Exercise With Concat And Reduce

I'm working on an exercise where, starting from an array of arrays, I have to reduce it (using reduce and concat) in a single array that contains all the elements of every single a

Solution 1:

i not have completely clear how reduce works yet

It works like this:

Array.prototype.reduce = function(callback, startValue){
    var initialized = arguments.length > 1,
        accumulatedValue = startValue;

    for(var i=0; i<this.length; ++i){
        if(i inthis){
            if(initialized){
                accumulatedValue = callback(accumulatedValue, this[i], i, this);
            }else{
                initialized = true;
                accumulatedValue = this[i];
            }
        }
    }

    if(!initialized)
        thrownewTypeError("reduce of empty array with no initial value");
    return accumulatedValue;
}

Your failing example does pretty much this:

vararray = [[1,2,3],[4,5,6],[7,8,9]];

var tmp = 0;
//and that's where it fails.//because `tmp` is 0 and 0 has no `concat` method
tmp = tmp.concat(array[0]);
tmp = tmp.concat(array[1]);
tmp = tmp.concat(array[2]);

var new_array = tmp;

replace the 0 with an Array, like [ 0 ]