This JavaScript exception can’t access the lexical declaration `variable’ before initialization occurs if a lexical variable has been accessed before initialization. This could happen inside any block statement when let or const declarations are accessed when they are undefined.
Message:
ReferenceError: Use before declaration (Edge)
ReferenceError: can't access lexical declaration `variable' before
initialization (Firefox)
ReferenceError: 'variable' is not defined (Chrome)
Error Type:
ReferenceError
Cause of the error: Somewhere in the code, there is a lexical variable that was accessed before initialization.
Example 1: In this example, the const keyword is used with the variable inside the if statement, So the error has occurred.
Javascript
function GFG() { const var_1 = "This is"; if (true) { const var_1 = var_1 + "neveropen"; }}function Geeks() { try { GFG(); console.log( "'Can't access lexical declaration" + "`variable'before initialization' " + "error has not occurred"); } catch (e) { console.log( "'Can't access lexical declaration" + "`variable' before initialization'" + " error has occurred"); }}Geeks() |
Output
'Can't access lexical declaration`variable' before initialization' error has occurred
Example 2: In this example, the keyword is used with the variable, So the error has occurred.
Javascript
function GFG() { let var_1 = 3; if (true) { var_1 = var_1 + 5; }}function Geeks() { try { GFG(); console.log( "'Can't access lexical declaration" + "`variable' before initialization'" + " error has not occurred"); } catch (e) { console.log( "'Can't access lexical declaration" + "`variable'before initialization'" + " error has occurred"); }}Geeks() |
Output
'Can't access lexical declaration`variable' before initialization' error has not occurred
