What makes the code below invalid in strict mode?
let x: string[];
if (Math.random() > .5){ x = ['x']; }
//TS2454: x possible undefined. Yeah, I know?
return x?.map(v => v);
Yes, it is acknowledged that x could potentially be undefined. However, this is why the Optional Chaining Operator is being utilized. It effectively handles cases where a variable may be undefined.
Strict mode flags an error due to TypeScript's strictNullChecks setting, preventing the use of uninitialized variables.
Your code exhibits this issue with variable x, which is declared but not necessarily initialized before being used in the return statement.
You have 3 potential solutions:
let x: string[] = [];
let x: string[] | undefined;
let x: string[];
if (Math.random() > .5) {
x = ['x'];
} else {
x = [];
}
return x.map(v => v);
Furthermore, there exists an alternate method to inform the compiler that you acknowledge the variable being uninitialized - provided you are certain it won't lead to any issues, prompting it to cease flagging errors of this nature:
let x!: string[];
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