var funcs = []
[1, 2].forEach( (i) => funcs.push( () => i ) )
Why does it produce the error below?
TypeError: Cannot read property 'forEach' of undefined
at Object.<anonymous>
However, the error goes away if the semicolon ; is added to the end of the first line.
There is no semicolon at the end of the first line. So the two lines run together, and it is interpreted as setting the value of funcs to
[][1, 2].forEach( (i) => funcs.push( () => i ) )
The expression 1, 2 becomes just 2 (comma operator), so you're trying to access index 2 of an empty array:
[][2] // undefined
And undefined has no forEach method. To fix this, always make sure you put a semicolon at the end of your lines (or if you don't, make sure you know what you're doing).
a, b, c, it evaluates all of the sub-expressions in order, a, then b, then c and then returns the value of the last sub-expression (c). This is useful e.g. when the previous expressions are only used for their side effects in a situation where only expressions are allowed, like the first line of a for loop.
we called the forEach method on an undefined value, we got the error.
const myarr = undefined;
// Initialize to empty array if falsy
const arr = myarr || [];
// Using optional chaining
arr?.forEach(element => {
console.log(element);
});
// Check if truthy
if (arr) {
arr.forEach(element => {
console.log(element);
});
}
// Check if Array
if (Array.isArray(arr)) {
arr.forEach(element => {
console.log(element);
});
}
Keep the semi-colon so the variable declaration of funcs does not include the anonymous array you instantiate as belonging to the variable and also, if you are simply trying to push all the elements of the array into 'funcs' then it should look like:
[1, 2].forEach( (i) => funcs.push(i) )
var funcs = [1, 2];Whenever we are using an array to loop over bunch of events, it is required to put semicolon to the previous line.
After we query the element we should end the line with semicolon
const el = document.getElementById("giri");
['click', 'touchend'].forEach(event => console.log(event))
I got the above error because I didn't put semicolon before the anonymous array
const el = document.getElementById("giri")
['click', 'touchend'].forEach(event => console.log(event))
Another solution to this problem is to avoid using anonymous array. No semicolons needed.
var funcs = []
var arr = [1, 2]
arr.forEach( (i) => funcs.push( () => i ) )Add semi-colon in the of first line
var funcs = []; //<-- ; semi-colon added here
[1, 2].forEach( (i) => funcs.push( () => i ) )
var funcs = [][1, 2].forEach....map()instead of.forEach()at single linevar funcs = [1, 2].map( (i) => () => i )to avoid issue with semicolon