Return from a for loop but keep loop running

Question

I have a for loop that needs to return something on every iteration:

for(var i=0;i<100;++i) {
 return i;
}

but return breaks the loop. How can I return but kee the loop running?

• tckmn: What do you expect it to return, then?
• stlvc: You can't. What you can do however, is push the return value to an array for example. Can you be more specific on what you want to achieve?
• Yoshi: Depending on your target system, yield could be a solution (so-question).
• nnnnnn: Return something to where? By definition a function only returns one "thing", though that "thing" may be an array or object that contains multiple values. (Unless yield works for your situation.)

Answer 1

Store it inside an array.

var array = [];
for (var i = 0; i < 100; ++i) {
 array.push(i);
}

• Geeky Guy: @Doorknob This is not Java.
• Mike Rifgin: thought as much. I can't use an array in this instance.
• tckmn: @MikeRifgin Then what do you want it to return?

Answer 2

The context here is unclear. If you are trying to execute a function for each iteration of the loop, why not something simple like calling a function from within the loop?

for(var i=0;i<100;++i) {
 processIteration(i)
}

In processIteration you could simply handle what you need to happen with that value.

Answer 3

Store the values you need to return in an array, then after the loop, return the array.

Answer 4

There are 3 ways to solve this

1. Promises

function loop() {
 promises = []
 for (var i = 0; i < 100; ++i) {
 // push a promise resolve to a promises array
 promises[i] = Promise.resolve(i);
 }
 return promises;
}
// Observe the promises loop
for (let p of loop()) {
 p.then(console.log)
}

2. Callbacks

function loop(cb) {
 for(var i = 0; i < 100; ++i) {
 // calling the callback 
 cb(i);
 }
}
// Pass a do something method
// Here it's the console log as the callback
loop(console.log)

3. Yield

// Generator function for loop over 100
function* loop() {
 for (var i = 0; i < 100; ++i) {
 // return value from loop 
 yield i;
 }
}
// Initialize the generator function
let it = loop();
// Call and get the resulr
// it.next().value
var result = it.next();
while (!result.done) {
 console.log(result.value); // 1 2 3 .... 99
 result = it.next();
}