IDE

A better typeof

#javascript,#todayilearned

The typeof operator is a really useful one but it has a few pitfalls:

typeof ["an", "array"] // object
typeof /regex/g // object
typeof null // object
typeof var NaN: numberNaN // number
typeof var Number: NumberConstructor
(value?: any) => number
An object that represents a number of any kind. All JavaScript numbers are 64-bit floating-point numbers.
Number('I am not a number!') // number

Ok, that's a lot of pitfalls;

But there is a way to get more detailed types using Object.prototype.toString.call() on a value:

// This statement basically means: "Call the toString method of the object prototype on whatever value you like"
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<{
    object: string;
}, [], string>(this: (this: {
    object: string;
}) => string, thisArg: {
    object: string;
}): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call({ object: stringobject: "true" }) // the infamous [object Object]
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<string[], [], string>(this: (this: string[]) => string, thisArg: string[]): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(["an", "array"]) // [object Array]
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<string, [], string>(this: (this: string) => string, thisArg: string): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call("a string") // [object String]
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<bigint, [], string>(this: (this: bigint) => string, thisArg: bigint): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(1n) // [object Bigint]
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<Date, [], string>(this: (this: Date) => string, thisArg: Date): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(new var Date: DateConstructor
new () => Date (+4 overloads)Date()) // [object Date] really
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<Error, [], string>(this: (this: Error) => string, thisArg: Error): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(new var Error: ErrorConstructor
new (message?: string | undefined, options?: ErrorOptions | undefined) => Error (+1 overload)Error("an error")) // [object Error]
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<() => void, [], string>(this: (this: () => void) => string, thisArg: () => void): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(function () {}) // [object Function]
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<() => Generator<never, void, unknown>, [], string>(this: (this: () => Generator<never, void, unknown>) => string, thisArg: () => Generator<never, void, unknown>): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(function* () {}) // [object GeneratorFunction]
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<RegExp, [], string>(this: (this: RegExp) => string, thisArg: RegExp): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(/regex/gi) // [object RegExp]
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<symbol, [], string>(this: (this: symbol) => string, thisArg: symbol): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(var Symbol: SymbolConstructor
(description?: string | number | undefined) => symbol
Returns a new unique Symbol value.
@paramdescription Description of the new Symbol object.
Symbol()) // [object Symbol]
var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<number, [], string>(this: (this: number) => string, thisArg: number): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(var NaN: numberNaN) // it's not perfect: [object Number]

Of course, this could be made a function (with a few finishing touches from here)

function function type(obj: any, showFullClass?: boolean): stringtype(obj: anyobj: any, showFullClass: booleanshowFullClass = false) {
    // Whether to return the whole type
    if (showFullClass: booleanshowFullClass && typeof obj: anyobj === "object") {
        return var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<any, [], string>(this: (this: any) => string, thisArg: any): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(obj: anyobj);
    }

    if (obj: anyobj == null) { return (obj: anyobj + '').String.toLowerCase(): string
Converts all the alphabetic characters in a string to lowercase.
toLowerCase(); } // implicit toString() conversion

    if (var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.is(value1: any, value2: any): boolean
Returns true if the values are the same value, false otherwise.
@paramvalue1 The first value.@paramvalue2 The second value.
is(obj: anyobj, var NaN: numberNaN)) return "nan";

    var function (local var) deepType: stringdeepType = var Object: ObjectConstructor
Provides functionality common to all JavaScript objects.
Object.ObjectConstructor.prototype: Object
A reference to the prototype for a class of objects.
prototype.Object.toString(): string
Returns a string representation of an object.
toString.CallableFunction.call<any, [], string>(this: (this: any) => string, thisArg: any): string
Calls the function with the specified object as the this value and the specified rest arguments as the arguments.
@paramthisArg The object to be used as the this object.@paramargs Argument values to be passed to the function.
call(obj: anyobj).String.slice(start?: number | undefined, end?: number | undefined): string
Returns a section of a string.
@paramstart The index to the beginning of the specified portion of stringObj.@paramend The index to the end of the specified portion of stringObj. The substring includes the characters up to, but not including, the character indicated by end.
If this value is not specified, the substring continues to the end of stringObj.
slice(8,-1).String.toLowerCase(): string
Converts all the alphabetic characters in a string to lowercase.
toLowerCase();
    if (function (local var) deepType: stringdeepType === 'generatorfunction') { return 'function' }

    // Prevent overspecificity (for example, [object HTMLDivElement], etc).
    // Account for functionish Regexp (Android <=2.3), functionish <object> element (Chrome <=57, Firefox <=52), etc.
    // String.prototype.match is universally supported.

    return function (local var) deepType: stringdeepType.String.match(matcher: {
    [Symbol.match](string: string): RegExpMatchArray | null;
}): RegExpMatchArray | null (+1 overload)
Matches a string or an object that supports being matched against, and returns an array
containing the results of that search, or null if no matches are found.
@parammatcher An object that supports being matched against.
match(/^(array|bigint|date|error|function|generator|regexp|symbol)$/) ? function (local var) deepType: stringdeepType :
       (typeof obj: anyobj === 'object' || typeof obj: anyobj === 'function') ? 'object' : typeof obj: anyobj;
}