How to concat string and number in Typescript

Question

I am using method to get data

function date() {
    let str = '';

    const currentTime = new Date();
    const year = currentTime.getFullYear();
    const month = currentTime.getMonth();
    const day = currentTime.getDate();

    const hours = currentTime.getHours();
    let minutes = currentTime.getMinutes();
    let seconds = currentTime.getSeconds();
    if (month < 10) {
        //month = '0' + month;
    }
    if (minutes < 10) {
        //minutes = '0' + minutes;
    }
    if (seconds < 10) {
        //seconds = '0' + seconds;
    }
    str += year + '-' + month + '-' + day + ' ' + hours + ':' + minutes + ':' + seconds + ' ';

    console.log(str);
}

And as output I get

2017-6-13 20:36:6

I would like to get the same thing, but like

2017-06-13 20:36:06

But if I try one of the lines, that I commented out, for example this one

month = '0' + month;

I get error

Argument of type 'string' is not assignable to parameter of type 'number'.

How could I concat string and number?

see also: https://stackoverflow.com/questions/10073699/pad-a-number-with-leading-zeros-in-javascript — Aprillion, Sep 22 '17 at 16:58

Tyler Miller · Answer 1 · 2019-06-06T22:19:49.527

67

Template literals (ES6+)

Instead of concatenation like month = '0' + month; You can use a template literal

const paddedMonth: string = `0${month}`;

Your string concatenation then turns into this for example:

str = `${year}-${paddedMonth}-${day} ${hours}:${minutes}:${seconds} `;

Much more readable, IMO.

Union Types

You can also use a union type when declaring variables.

let month: string | number = currentTime.getMonth();

if (month < 10) {
  month = '0' + month;
}

edited Jun 06 '19 at 22:19

answered Jul 13 '17 at 18:50

Tyler Miller

896
6
18

That's a good idea - unless the OP is pushing this out to the web and wants to support IE: https://caniuse.com/#search=template%20literals – abagshaw Jul 13 '17 at 19:31
5

If TypeScript is being used, it will convert template literals to regular string concatenation when compiling for non-es6. – libertyernie Jul 14 '17 at 14:13

score 4 · Answer 2 · answered Jul 13 '17 at 18:57

if you want to work with date, you can use momentjs module: https://momentjs.com

moment().format('MMMM Do YYYY, h:mm:ss a'); // July 13th 2017, 11:18:05 pm
moment().format('dddd');                    // Thursday
moment().format("MMM Do YY");               // Jul 13th 17
moment().format('YYYY [escaped] YYYY');     // 2017 escaped 2017
moment().format();                          // 2017-07-13T23:18:05+04:30

and about the error you got,you most use like this:

 let monthStr: string = month;
 if ( month < 10) {
     monthStr = '0' + month;
 }

abagshaw · Answer 3 · 2017-07-13T19:05:29.237

First of all, I'm not sure why you are defining month as a const and then trying to change it. Declare all your variables with let and convert them all to strings and you should be good to go.

function date() {
    let str = '';

    const currentTime = new Date();
    let year = currentTime.getFullYear().toString();
    let month = currentTime.getMonth().toString();
    let day = currentTime.getDate().toString();

    let hours = currentTime.getHours().toString();
    let minutes = currentTime.getMinutes().toString();
    let seconds = currentTime.getSeconds().toString();
    if (month < 10) {
        month = '0' + month;
    }
    if (minutes < 10) {
        minutes = '0' + minutes;
    }
    if (seconds < 10) {
        seconds = '0' + seconds;
    }
    str += year + '-' + month + '-' + day + ' ' + hours + ':' + minutes + ':' + seconds + ' ';

    console.log(str);
}

See it working here: https://jsfiddle.net/40jbg8qt/

can you change type of `month` from number to string in typescript when you use `let`? — Aprillion, Sep 22 '17 at 16:55

score 0 · Answer 4 · edited Feb 19 '18 at 18:04

0

You could use something like this:

let pais:string = 'Ecuador';
let codigo:number = 593;
let opcionUno:string = this.pais + this.number
let opcionDos:string = this.pais.concat(this.number);

edited Feb 19 '18 at 18:04

Avery

2,035
4
33
32

answered Feb 19 '18 at 17:53

martosfre

191
2
6

score -1 · Answer 5 · answered Jul 14 '17 at 14:12

-1

You could also do something like this:

let month: string | number = currentTime.getMonth();
if (month < 10) month = '0' + month;

Or this:

const month = currentTime.getMonth();
const monthStr = (month < 10 ? "0" : "") + month;

answered Jul 14 '17 at 14:12

libertyernie

2,312
1
10
11

How to concat string and number in Typescript

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