How do I loop through each member of each array in another array?

Say there's an array of arrays.

n = [ a = ["foo","bar"],
      b = ["foo2","bar2"],
      c = ["foo3","bar3"],
      d = ["foo4","bar4"],
      e 开发者_运维技巧= ["foo5","bar5"] ]

What's the simplest syntax to loop through all the foos and bars?

If you always have exactly 2 things in the inner arrays as per your example (fiddle - http://jsfiddle.net/pvqtz/):

for (var index = 0; index < n.length; index++) {
    var foobar = n[index];
    var foo = foobar[0];
    var bar = foobar[1];
    alert(foo + bar);
}

For an arbitrary number of things, use a nested loop (fiddle - http://jsfiddle.net/pvqtz/1/):

for (var index = 0; index < n.length; index++) {
    var innerArray = n[index];
    for (var innerIndex = 0; innerIndex < innerArray.length; innerIndex++) {
        var elem = innerArray[innerIndex];
        alert(elem);
    }
}

If your environment supports it, I tend to like forEach for this:

n.forEach(function(n2) { 
    n2.forEach(function(val) {
        console.log(val) 
    })
});

and just for the heck of it, if you're dealing with nested arrays of arbitrary depth, you can recurse:

function visit(a, f) {
    if (Array.isArray(a)) {
        a.forEach(function(a2) { 
            visit(a2, f)
        })
    } else f(a);
}

n = ["foo",["foo1", "bar1"], ["foo2", ["foo3","bar3"]]];
visit(n, function(val) { console.log(val) });

To iterate over foos and bars in one loop:

var i = -1;
while (i++ < n.length) 
    alert (n[i][0]+":"+n[i][1]);

or

for (var i = 0; i < n.length; i++) 
    alert (n[i][0]+":"+n[i][1]);

To iterate over all foos, then over all bars:

var i = -1, j = -1;
while (i++ < 2) 
    while (j++ < n.length) 
        alert (n[j][i]);

or

for (var i = 0; i < 2; i++) 
    for (var j = 0; j < n.length; j++) 
        alert (n[j][i]);