How to Sleep in TypeScript

1. Use Blocking to Sleep a Thread in TypeScript
2. Use Promises to Sleep in TypeScript

While implementing business logic, it is often needed to add a delay to a function or sleep for some time waiting for some API call.

This tutorial will discuss different ways and concepts behind sleeping a thread in TypeScript.

Use Blocking to Sleep a Thread in TypeScript

Blocking can be used to wait for some time in a synchronous manner. The following code sample demonstrates how a thread can be blocked, so execution happens after some seconds.

function delayBlocking(milliseconds: number){
    const timeInitial : Date = new Date();
    var timeNow : Date = new Date();
    for ( ; timeNow - timeInitial < milliseconds; ){
        timeNow = new Date();
    }
    console.log('Sleep done!');
}

console.log('Starting, will sleep for 5 secs now');
delayBlocking(5000);
console.log('Normal code execution continues now');

Output:

Starting, will sleep for 5 secs now
Sleep done!
Normal code execution continues now

The above code segment will sure stop execution for some time, but sometimes this is not the desired effect as for a large delay, the entire code will be blocked.

Use Promises to Sleep in TypeScript

The setTimeout function is used to resolve a Promise after some delay. This method can be chained with then or async...await. The following code segment shows behavior with then.

function delay(milliseconds : number) {
    return new Promise(resolve => setTimeout( resolve, milliseconds));
}

console.log('Starting, will sleep for 5 secs now');
delay(5000).then(() => console.log('Normal code execution continues now') );

With async..await it can be implemented according to the following code segment-

function delay(milliseconds : number) {
    return new Promise(resolve => setTimeout( resolve, milliseconds));
}
( async() => {
    console.log('Starting, will sleep for 5 secs now');
    await delay(5000);
    console.log('Normal code execution continues now');
})();