There’s hardly ever a reason for using = over = – if you’re comparing to true or false and you want coercion (for example you want 0 or '' to evaluate to false) then just use if(! empty_str) rather than if(empty_str = false). typeof typeof typeof A js data type 'number', 'string', 'boolean', 'object', 'function', 'undefined', 'symbol', 'bigint' // Number. The thinking is that you can either think about whether to use = or = every time you check for equality, or you can just get into the habit of always writing =. We can not use the typeof operator as it returns object for both arrays and objects in JavaScript. The recommendation from Crockford is that it’s safer to use = in many circumstances, and that if you’re going to use it in some circumstances it’s better to be consistent and use it for everything. Below is the reason why you may want to use = anyway.

It was written in TSX (TypeScript's implementation of JSX) and makes use of a type alias and a type query to obtain the type of all properties provided.To answer the main question – there is no danger in using typeof with =. Here is how you use it when you're evaluating the type of a number, 007. It evaluates the type of the operand and returns the result as a string. The JavaScript typeof Operator The typeof operator takes only one operand (a unary operator). Obtain the type of `rectangle1` and call it `Rectangle` type Rectangle = typeof rectangle1 įor a practical example, take a look at this strongly typed React component. An object is a collection of key-value pairs. As of ECMAScript 2015, typeof always returns one of seven possible string values: typeof undefined // 'undefined' typeof true // 'boolean' typeof 1337 // 'number' typeof 'foo' // 'string' typeof JavaScript has the typeof operator which returns the type of its operand as a string. Despite the same name, it is very different from JavaScript's typeof operator - in fact, the two can only appear in mutually exclusive places. TypeScript uses the typeof keyword for capturing anonymous types.

Type Queries and typeof in TypeScript May 31, 2016

Js typeof object