Question

just wanting to set up an array through my parameters. Check out this pseudocode bellow to see what I’m trying to do:

function someFunction(x = new Array()){
 for (a in x){
  some action with x[a];
 }
}

someFunction([value a, value b, value c]);

So I’m trying to do something that may work similar to this. Thanks in advance guys!

Answer 1

That’s basically a special case of each:

function each(a, f) {
    a = a || [];
    for (var i=0; i < a.length; ++i) {
        f(a[i]);
    }
}

though each is usually implemented as a method of Array, along with map, filter and reduce/fold:

Array.prototype.each = function(f) {
    for (var i=0; i < this.length; ++i) {
        f(this[i], i);
    }
};

Array.prototype.map = function(f) {
    var result = [];
    for (var i=0; i < this.length; ++i) {
        result[i] = f(this[i], i);
    }
    return result;
};

Array.prototype.map = function(keep) {
    var result = [];
    for (var i=0; i < this.length; ++i) {
        if (keep(this[i], i)) {
            result.push(this[i]);
        }
    }
    return result;
};

Array.prototype.foldl = function(f) {
    var result = this[0];
    for (var i=1; i < this.length; ++i) {
        result = f(result, this[i]);
    }
    return result;
};

Array.prototype.foldr = function(f) {
    var i=this.length-1
    var result = this[i];
    for (--i; i >= 0; --i) {
        result = f(this[i], result);
    }
    return result;
};

Array.prototype.reduce = Array.prototype.foldl;

Note that using for (... in ...) with arrays can cause problems as it will pick up properties defined on an array in addition to the integer indices.