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?

Answer 1

Union Types

You can use a union type when declaring variables.

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

Template literals (ES6+)

Alternatively you can create a new variable and 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.

Answer 2

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;  }