time-to-botec

README.md (5340B)

---

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 # whileAsync
 
 > Invoke a function while a test condition is true.
 
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 <section class="usage">
 
 ## Usage
 
 ```javascript
 var whileAsync = require( '@stdlib/utils/async/while' );
 ```
 
 #### whileAsync( predicate, fcn, done\[, thisArg ] )
 
 Invokes a `function` until a `predicate` function returns `false`.
 
 ```javascript
 function predicate( i, clbk ) {
     clbk( null, i < 5 );
 }
 
 function fcn( i, next ) {
     setTimeout( onTimeout, 0 );
     function onTimeout() {
         console.log( 'beep: %d', i );
         next();
     }
 }
 
 function done( error ) {
     if ( error ) {
         throw error;
     }
 }
 
 whileAsync( predicate, fcn, done );
 /* =>
     beep: 0
     beep: 1
     beep: 2
     beep: 3
     beep: 4
 */
 ```
 
 The `predicate` function is provided two arguments:
 
 -   `i`: iteration number (starting from zero)
 -   `clbk`: a callback indicating whether to invoke `fcn`
 
 The `clbk` function accepts two arguments:
 
 -   `error`: error object
 -   `bool`: test result
 
 If the test result is truthy, the function invokes `fcn`; otherwise, the function invokes the `done` callback.
 
 The function to invoke is provided two arguments:
 
 -   `i`: iteration number (starting from zero)
 -   `next`: a callback which must be invoked before proceeding to the next iteration
 
 The first argument of both `clbk` and `next` is an `error` argument. If either function is called with a truthy `error` argument, the function suspends execution and immediately calls the `done` callback for subsequent `error` handling.
 
 ```javascript
 function predicate( i, clbk ) {
     clbk( null, i < 5 );
 }
 
 function fcn( i, next ) {
     setTimeout( onTimeout, 0 );
     function onTimeout() {
         next( new Error( 'beep' ) );
     }
 }
 
 function done( error ) {
     console.error( error.message );
     // => beep
 }
 
 whileAsync( predicate, fcn, done );
 ```
 
 The `done` callback is invoked with an `error` argument and any arguments passed to the final `next` callback.
 
 ```javascript
 function predicate( i, clbk ) {
     clbk( null, i < 5 );
 }
 
 function fcn( i, next ) {
     setTimeout( onTimeout, 0 );
     function onTimeout() {
         next( null, i );
     }
 }
 
 function done( error, result ) {
     if ( error ) {
         throw error;
     }
     console.log( result );
     // => 4
 }
 
 whileAsync( predicate, fcn, done );
 ```
 
 To set the function execution context for the invoked function, provide a `thisArg`.
 
 <!-- eslint-disable no-invalid-this -->
 
 ```javascript
 function predicate( i, clbk ) {
     clbk( null, i < 5 );
 }
 
 function fcn( i, next ) {
     this.count += 1;
     setTimeout( onTimeout, 0 );
     function onTimeout() {
         next();
     }
 }
 
 var context = {
     'count': 0
 };
 
 whileAsync( predicate, fcn, done, context );
 
 function done( error ) {
     if ( error ) {
         throw error;
     }
     console.log( context.count );
     // => 5
 }
 ```
 
 </section>
 
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 <section class="notes">
 
 ## Notes
 
 -   Execution is **not** guaranteed to be asynchronous. To guarantee asynchrony, wrap the `done` callback in a function which either executes at the end of the current stack (e.g., `nextTick`) or during a subsequent turn of the event loop (e.g., `setImmediate`, `setTimeout`).
 
 </section>
 
 <!-- /.notes -->
 
 <!-- Package usage examples. -->
 
 <section class="examples">
 
 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var repeatString = require( '@stdlib/string/repeat' );
 var whileAsync = require( '@stdlib/utils/async/while' );
 
 function predicate( i, clbk ) {
     setTimeout( onTimeout, 0 );
     function onTimeout() {
         clbk( null, i < 5 );
     }
 }
 
 function fcn( i, next ) {
     setTimeout( onTimeout, 0 );
     function onTimeout() {
         next( null, repeatString( 'beep', i+1 ) );
     }
 }
 
 function done( error, result ) {
     if ( error ) {
         throw error;
     }
     console.log( result );
 }
 
 whileAsync( predicate, fcn, done );
 ```
 
 </section>
 
 <!-- /.examples -->
 
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