In the realm of JavaScript, certain values are known as "falsy". These include:
- false
- 0
- ''
- ""
- null
- undefined
- NaN
But how does TypeScript treat the not operator (!)? Is it similar to JavaScript or different?
In the realm of JavaScript, certain values are known as "falsy". These include:
But how does TypeScript treat the not operator (!)? Is it similar to JavaScript or different?
One of the main objectives outlined in the principles behind TypeScript is:
To maintain the runtime behavior of all JavaScript code.
This indicates that every piece of JavaScript code will exhibit the same behavior when written in TypeScript. Even though there may be additional semantic errors, the underlying behavior remains consistent.
Therefore, if you ever question whether an operator like ! performs differently in TS, rest assured that it always behaves consistently.
JavaScript emitted will function equivalently to JavaScript in every scenario.
Regarding the types that the compiler identifies as falsy during design time, almost everything is considered falsy except for NaN:
const f0 = !false // true
const f1 = !0; // true
const f2 = !0n; // true
const f3 = !""; // true
const f4 = !null; // true
const f5 = !undefined; // true
const f6 = !NaN; // boolean (no NaN type in TypeScript)
At present, TypeScript lacks a numeric literal type representation of NaN; it is merely viewed as type number. Since a number can be either truthy or falsy, the expression !NaN results in a type of boolean. There exists a pending proposal named microsoft/TypeScript#28682 suggesting the introduction of numeric literals for NaN, Infinity, and -Infinity, although its implementation status remains uncertain.
Hoping this explanation proves beneficial to you. Best of luck!
TypeScript expands upon the capabilities of JavaScript.
By introducing new features, TypeScript enhances the power of JavaScript without altering its existing functionalities.
Anything that is considered untrue in JavaScript remains untrue in TypeScript. Likewise, anything deemed true in JavaScript holds true in TypeScript as well.
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