Message
ReferenceError: Use before delaration (Edge) ReferenceError: can't access lexical declaration `X' before initialization (Firefox) ReferenceError: 'x' is not defined (Chrome)
Error type
What went wrong?
A lexical variable was accessed before it was initialized. This happens within any block statement, when let or const declarations are accessed before they are defined.
Examples
Invalid cases
In this case, the variable "foo" is redeclared in the block statement using let.
function test() {
let foo = 33;
if (true) {
let foo = (foo + 55);
// ReferenceError: can't access lexical
// declaration `foo' before initialization
}
}
test();
Valid cases
To change "foo" inside the if statement, you need to remove the let that causes the redeclaration.
function test(){
let foo = 33;
if (true) {
foo = (foo + 55);
}
}
test();