I have a function that loops through a list using forEach and I want to return a result early (mimicking break). But the function returns undefined. Why does it return undefined?
const list = [1, 2, 3];
const test = () => {
const rs = list.forEach(item => {
return item
})
return rs
}
const rs = test()
console.log(rs)
The function forEach does not return a value. You'd be better off using find. At this point, it's unclear what you want to do with your loop so I'm assuming that you are trying to return a value based on a condition.
From MDN
forEach() executes the callback function once for each array element; unlike map() or reduce() it always returns the value undefined and is not chainable. The typical use case is to execute side effects at the end of a chain.
Also, the way you are calling your function is wrong. You are setting a variable inside a callback but never returning the variable. The test function returns nothing. Hence you get undefined.
You should return the value of the find function.
const list = [1, 2, 3];
const test = () => {
return list.find(item => {
if(/* some condition */ item > 1) {
return item
}
})
}
const rs = test()
console.log(rs)If you want to know if there is something in the list you need this - note test needs to return something for the log to show anything
const list = [1, 2, 3];
const test = () => {
const rs = list.filter(item => {
return item!=null
})
return rs.length>0;
}
const rs = test()
console.log(rs)
By definition, forEach return undefined. see this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach
you can use map instead,which returns an array and do not forget to return it in a map
const list = [1, 2, 3];
const test = () => {
const rs = list.map(item => {
return item
})
return rs;
}
const rs = test()
Fix this problem this way.
const list = [1, 2, 3];
const test = () => {
const rs = [];
list.forEach(item => {
rs.push(item);
})
return rs;
}
const rs = test();
console.log(rs);