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I'm trying to set the variable value when it's undefined however, I'm getting an error while trying to use vanilla javascript approach.
Block-scoped variable 'x' used before its declaration.
What is the best approach when using typescript for setting undefined variable?
let x = (typeof x === 'undefined') ? def_val : x;
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YES, you can, because undefined is defined as undefined.
To make a variable null we must assign null value to it as by default in typescript unassigned values are termed undefined. We can use typeof or '==' or '===' to check if a variable is null or undefined in typescript.
TypeScript has a powerful system to deal with null or undefined values. By default null and undefined handling is disabled, and can be enabled by setting strictNullChecks to true.
To set the value of a variable is it's equal to undefined , use the nullish coalescing operator, e.g. myVar = myVar ?? 'new value' . The operator returns the right-hand side operand if the left-hand side evaluates to undefined or null , otherwise it returns the left-hand side operand. Copied!
The logical nullish assignment (x ??= y) operator only assigns if x is nullish (null or undefined).
x ??= default_value
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