checkTypes.ts

const types = {
    obj: 'Object',
    arr: 'Array',
    str: 'String',
    num: 'Number',
    func: 'Function',
    bool: 'Boolean',
    nil: 'Null',
    undef: 'Undefined',
    date: 'Date',
    reg: 'RegExp',
};

export function getType(value: any): string {
    return Object.prototype.toString.call(value).slice(8, -1);
}

export function isObject<P = {}>(value: any): value is P {
    return getType(value) === types.obj;
}

export function isArray<P = any>(value: any): value is P[] {
    return getType(value) === types.arr;
}

export function isArrayClassic<P = any>(value: any): value is P[] {
    return Array.isArray(value);
}

export function isString(value: any): value is string {
    return getType(value) === types.str;
}

export function isStringClassic(value: any): value is string {
    return typeof value === 'string';
}

export function isNumber(value: any): value is number {
    return getType(value) === types.num;
}

export function isNumberClassic(value: any): value is number {
    return typeof value === 'number';
}

export function isFunction(value: any): value is Function {
    return getType(value) === types.func;
}

export function isFunctionClassic(value: any): value is Function {
    return typeof value === 'function';
}

export function isBoolean(value: any): value is boolean {
    return getType(value) === types.bool;
}

export function isBooleanClassic(value: any): value is boolean {
    return typeof value === 'boolean';
}

export function isNull(value: any): value is null {
    return getType(value) === types.nil;
}

export function isNullClassic(value: any): value is null {
    return value === null;
}

export function isUndefined(value: any): value is undefined {
    return getType(value) === types.undef;
}

export function isUndefinedClassic(value: any): value is undefined {
    return typeof value === 'undefined';
}

export function isNil(value: any): value is null | undefined {
    return value == null;
}

export function isRegExp(value: any): value is RegExp {
    return getType(value) === types.reg;
}

export function isDate(value: any): value is Date {
    return getType(value) === types.date;
}

todo: Map, Set, экземпляр класса, NaN(?), Finite(?)