How do I express a date type in TypeScript? - date

Question

How do I express dates in TypeScript? Dates aren't a TypeScript type, so do I use any or object? Seems like there would be a "right" way to do:
let myDate: any = new Date();
I couldn't find much on Google, despite it being such a simple question.

Answer 1

The type is Date:
const d: Date = new Date(); // but the type can also be inferred from "new Date()" already
It is the same as with every other object instance :)

Answer 2

Every class or interface can be used as a type in TypeScript.
const date = new Date();
will already know about the date type definition as Date is an internal TypeScript object referenced by the DateConstructor interface.
And for the constructor you used, it is defined as:
interface DateConstructor {
new(): Date;
...
}
To make it more explicit, you can use:
const date: Date = new Date();
You might be missing the type definitions though, the Date is coming for my example from the ES6 lib, and in my tsconfig.json I have defined:
"compilerOptions": {
"target": "ES6",
"lib": [
"es6",
"dom"
],
You might adapt these settings to target your wanted version of JavaScript.
The Date is by the way an Interface from lib.es6.d.ts:
/** Enables basic storage and retrieval of dates and times. */
interface Date {
/** Returns a string representation of a date. The format of the string depends on the locale. */
toString(): string;
/** Returns a date as a string value. */
toDateString(): string;
/** Returns a time as a string value. */
toTimeString(): string;
/** Returns a value as a string value appropriate to the host environment's current locale. */
toLocaleString(): string;
/** Returns a date as a string value appropriate to the host environment's current locale. */
toLocaleDateString(): string;
/** Returns a time as a string value appropriate to the host environment's current locale. */
toLocaleTimeString(): string;
/** Returns the stored time value in milliseconds since midnight, January 1, 1970 UTC. */
valueOf(): number;
/** Gets the time value in milliseconds. */
getTime(): number;
/** Gets the year, using local time. */
getFullYear(): number;
/** Gets the year using Universal Coordinated Time (UTC). */
getUTCFullYear(): number;
/** Gets the month, using local time. */
getMonth(): number;
/** Gets the month of a Date object using Universal Coordinated Time (UTC). */
getUTCMonth(): number;
/** Gets the day-of-the-month, using local time. */
getDate(): number;
/** Gets the day-of-the-month, using Universal Coordinated Time (UTC). */
getUTCDate(): number;
/** Gets the day of the week, using local time. */
getDay(): number;
/** Gets the day of the week using Universal Coordinated Time (UTC). */
getUTCDay(): number;
/** Gets the hours in a date, using local time. */
getHours(): number;
/** Gets the hours value in a Date object using Universal Coordinated Time (UTC). */
getUTCHours(): number;
/** Gets the minutes of a Date object, using local time. */
getMinutes(): number;
/** Gets the minutes of a Date object using Universal Coordinated Time (UTC). */
getUTCMinutes(): number;
/** Gets the seconds of a Date object, using local time. */
getSeconds(): number;
/** Gets the seconds of a Date object using Universal Coordinated Time (UTC). */
getUTCSeconds(): number;
/** Gets the milliseconds of a Date, using local time. */
getMilliseconds(): number;
/** Gets the milliseconds of a Date object using Universal Coordinated Time (UTC). */
getUTCMilliseconds(): number;
/** Gets the difference in minutes between the time on the local computer and Universal Coordinated Time (UTC). */
getTimezoneOffset(): number;
/**
* Sets the date and time value in the Date object.
* #param time A numeric value representing the number of elapsed milliseconds since midnight, January 1, 1970 GMT.
*/
setTime(time: number): number;
/**
* Sets the milliseconds value in the Date object using local time.
* #param ms A numeric value equal to the millisecond value.
*/
setMilliseconds(ms: number): number;
/**
* Sets the milliseconds value in the Date object using Universal Coordinated Time (UTC).
* #param ms A numeric value equal to the millisecond value.
*/
setUTCMilliseconds(ms: number): number;
/**
* Sets the seconds value in the Date object using local time.
* #param sec A numeric value equal to the seconds value.
* #param ms A numeric value equal to the milliseconds value.
*/
setSeconds(sec: number, ms?: number): number;
/**
* Sets the seconds value in the Date object using Universal Coordinated Time (UTC).
* #param sec A numeric value equal to the seconds value.
* #param ms A numeric value equal to the milliseconds value.
*/
setUTCSeconds(sec: number, ms?: number): number;
/**
* Sets the minutes value in the Date object using local time.
* #param min A numeric value equal to the minutes value.
* #param sec A numeric value equal to the seconds value.
* #param ms A numeric value equal to the milliseconds value.
*/
setMinutes(min: number, sec?: number, ms?: number): number;
/**
* Sets the minutes value in the Date object using Universal Coordinated Time (UTC).
* #param min A numeric value equal to the minutes value.
* #param sec A numeric value equal to the seconds value.
* #param ms A numeric value equal to the milliseconds value.
*/
setUTCMinutes(min: number, sec?: number, ms?: number): number;
/**
* Sets the hour value in the Date object using local time.
* #param hours A numeric value equal to the hours value.
* #param min A numeric value equal to the minutes value.
* #param sec A numeric value equal to the seconds value.
* #param ms A numeric value equal to the milliseconds value.
*/
setHours(hours: number, min?: number, sec?: number, ms?: number): number;
/**
* Sets the hours value in the Date object using Universal Coordinated Time (UTC).
* #param hours A numeric value equal to the hours value.
* #param min A numeric value equal to the minutes value.
* #param sec A numeric value equal to the seconds value.
* #param ms A numeric value equal to the milliseconds value.
*/
setUTCHours(hours: number, min?: number, sec?: number, ms?: number): number;
/**
* Sets the numeric day-of-the-month value of the Date object using local time.
* #param date A numeric value equal to the day of the month.
*/
setDate(date: number): number;
/**
* Sets the numeric day of the month in the Date object using Universal Coordinated Time (UTC).
* #param date A numeric value equal to the day of the month.
*/
setUTCDate(date: number): number;
/**
* Sets the month value in the Date object using local time.
* #param month A numeric value equal to the month. The value for January is 0, and other month values follow consecutively.
* #param date A numeric value representing the day of the month. If this value is not supplied, the value from a call to the getDate method is used.
*/
setMonth(month: number, date?: number): number;
/**
* Sets the month value in the Date object using Universal Coordinated Time (UTC).
* #param month A numeric value equal to the month. The value for January is 0, and other month values follow consecutively.
* #param date A numeric value representing the day of the month. If it is not supplied, the value from a call to the getUTCDate method is used.
*/
setUTCMonth(month: number, date?: number): number;
/**
* Sets the year of the Date object using local time.
* #param year A numeric value for the year.
* #param month A zero-based numeric value for the month (0 for January, 11 for December). Must be specified if numDate is specified.
* #param date A numeric value equal for the day of the month.
*/
setFullYear(year: number, month?: number, date?: number): number;
/**
* Sets the year value in the Date object using Universal Coordinated Time (UTC).
* #param year A numeric value equal to the year.
* #param month A numeric value equal to the month. The value for January is 0, and other month values follow consecutively. Must be supplied if numDate is supplied.
* #param date A numeric value equal to the day of the month.
*/
setUTCFullYear(year: number, month?: number, date?: number): number;
/** Returns a date converted to a string using Universal Coordinated Time (UTC). */
toUTCString(): string;
/** Returns a date as a string value in ISO format. */
toISOString(): string;
/** Used by the JSON.stringify method to enable the transformation of an object's data for JavaScript Object Notation (JSON) serialization. */
toJSON(key?: any): string;
}

Answer 3

Typescript recognizes the Date interface out of the box - just like you would with a number, string, or custom type. So Just use:
myDate : Date;

Answer 4

As others have mentioned the type is Date.
This type is usefull when you want to enforce at compile time that you really have a Date object. Below is a mistake that is often make (forgetting the new keyword) and we can see that it is caught at compile time.
const date: Date = new Date();
function logDayNumber(date: Date){
console.log(date.getDay())
}
// Works fine
logDayNumber(date);
// Compile time error which happens when you forget new a String we be produced from Date()
// Argument of type 'string' is not assignable to parameter of type 'Date'
logDayNumber(Date());