How to solve TypeScript possibly undefined value

Example:

onsider a simple function declaration like:

typescriptCopy code

function myFunction(b: number, c?: number): number { return (b * c); }

When running the code with the above function declaration, a runtime error message ‘undefined’ may occur. Since we designated the second parameter ‘c’ as optional, it may or may not receive a value in the function call. If the function is called as myFunction(10), the value of ‘c’ will be undefined. To address this issue, we fundamentally need to write code to handle the scenario when the value of ‘c’ is undefined, and this can be accomplished in various ways.”

Key 1:

We can allocate a default value to c

For example:

typescriptCopy code

function myFunction(b: number, c: number = 20): number { return (b * c); }

“If you encounter this error in a modified scenario, such as when generating a component within an application, you can provide a default value or assign a value in the constructor.”

Key 2:

“You can utilize the bang(!) operator.

By employing the bang(!) operator, we affirm that the variable to which we apply the operator will never be null or undefined.”

For example:

function myFunction(b: number, c?: number): number {

    return (b * c!);

Key 3:

We can use an if statement to hold the situation where c is undefined.

For example:

typescriptCopy code

function myFunction(b: number, c?: number): number { if (c === undefined) { return 200; } else { return (b * c); } }

“We can also use alternative forms of if statements, such as the ternary operator (??). If you are certain that the property cannot have a value of null, you can use the non-null assertion operator, denoted by exclamation marks in TypeScript.

This operator removes null and undefined from any type without explicit type checking, indicating to TypeScript that the value can never be null or undefined.

In an if statement, you can also employ the logical AND (&&) operator to ensure that the property is of the correct type. The logical AND operator ensures the property is not undefined. This is necessary because if the reference is null or undefined, the chaining operator (?.) will return undefined, and TypeScript does not permit comparing undefined to a number.

The result might have a value of undefined due to the optional chaining operator, and the logical AND operator will not evaluate any value to the right if the value to the left is false or undefined.

All values in the if condition must be true for the if block to execute. Truthy values are those that are not false. This is why TypeScript can infer the type of the result variable as a string in the if block.” A better way to get around the error typescript: object is possibly ‘undefined’ situation is to use the type of operator.

For example

type b = {
c?: {
d?: string;
e?: string;
};
};

const p1: b = {};

if (p1.c && typeof p1.c.d === ‘string’) {
// 👇️ const result: string
const result = p1.c.d;
}
“We verify if the type is a string. This approach is superior to checking if the value is truthy, as empty strings are falsy values in TypeScript.

This error may manifest in various scenarios. While the error message remains consistent, its context may differ based on the location.”

1 thought on “How to solve TypeScript possibly undefined value”

Keerthy

GOOD POST

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