How to get the last item in a javascript-value object with a for loop?
for-loop, javascript, json
Solution
don't use `for (key in obj)`, it will iterate over all enumerable properties including prototype properties, and can lead to amazingly horrible things. Modern JS has a special function for getting only the relevant keys out of an object, using Object.keys(...), so if you use `var keys = Object.keys(obj)` to get the list of keys as an array, you can then iterate over that:
// blind iteration
Object.keys(obj).forEach(function(key, i) {
var value = obj[key];
// do what you need to here, with index i as position information.
// Note that you cannot break out of this iteration, although you
// can of course use ".some()" rather than ".forEach()" for that.
});
// indexed iteration
for(var keys = Object.keys(obj), i = 0, end = keys.length; i < end; i++) {
var key = keys[i], value = obj[key];
// do what you need to here, with index i as position information,
// using "break" if you need to cut the iteration short.
});
or select its last element immediately
var keys = Object.keys(obj);
var last = keys[keys.length-1];
or using a slice:
var keys = Object.keys(obj);
var last = keys.slice(-1)[0];
or using a shift (but that's a destructive operation, so we're not caching the keys because the shift turns it into "not all the keys anymore"):
var last = Object.keys(obj).shift();
2021 edit
There is now also the Object.entries function, which gets you key/value pairs in one go:
Object.entries(obj).forEach(([key, value]) => {
console.log(`key "${key}" points to:`, value):
});
Problem
``` var obj = { 'a' : 'apple', 'b' : 'banana', 'c' : 'carrot' } ``` If I do a ``` for (var key in obj) { console.log( key + ' has a value ' + obj[key] ); } ``` It will look through all the values in `obj`. If I have a much larger object, how do I know if I am on the last iteration of that `for` loop? I realize that key value pairs aren't really organized in order, but I need to accomplish something in the very last iteration of this loop and don't know how.