18bc768116
* Adding graphql query to fetch latest helm release of specified type * Updating typescript version and js file * Fixing PR comments in release * Adding feature flag as environment variable in release * Changing feature flag name * Updating files as per latest changes in master after resolving merge conflicts * Removing non prod modules
80 lines
1.7 KiB
Markdown
80 lines
1.7 KiB
Markdown
# once
|
|
|
|
Only call a function once.
|
|
|
|
## usage
|
|
|
|
```javascript
|
|
var once = require('once')
|
|
|
|
function load (file, cb) {
|
|
cb = once(cb)
|
|
loader.load('file')
|
|
loader.once('load', cb)
|
|
loader.once('error', cb)
|
|
}
|
|
```
|
|
|
|
Or add to the Function.prototype in a responsible way:
|
|
|
|
```javascript
|
|
// only has to be done once
|
|
require('once').proto()
|
|
|
|
function load (file, cb) {
|
|
cb = cb.once()
|
|
loader.load('file')
|
|
loader.once('load', cb)
|
|
loader.once('error', cb)
|
|
}
|
|
```
|
|
|
|
Ironically, the prototype feature makes this module twice as
|
|
complicated as necessary.
|
|
|
|
To check whether you function has been called, use `fn.called`. Once the
|
|
function is called for the first time the return value of the original
|
|
function is saved in `fn.value` and subsequent calls will continue to
|
|
return this value.
|
|
|
|
```javascript
|
|
var once = require('once')
|
|
|
|
function load (cb) {
|
|
cb = once(cb)
|
|
var stream = createStream()
|
|
stream.once('data', cb)
|
|
stream.once('end', function () {
|
|
if (!cb.called) cb(new Error('not found'))
|
|
})
|
|
}
|
|
```
|
|
|
|
## `once.strict(func)`
|
|
|
|
Throw an error if the function is called twice.
|
|
|
|
Some functions are expected to be called only once. Using `once` for them would
|
|
potentially hide logical errors.
|
|
|
|
In the example below, the `greet` function has to call the callback only once:
|
|
|
|
```javascript
|
|
function greet (name, cb) {
|
|
// return is missing from the if statement
|
|
// when no name is passed, the callback is called twice
|
|
if (!name) cb('Hello anonymous')
|
|
cb('Hello ' + name)
|
|
}
|
|
|
|
function log (msg) {
|
|
console.log(msg)
|
|
}
|
|
|
|
// this will print 'Hello anonymous' but the logical error will be missed
|
|
greet(null, once(msg))
|
|
|
|
// once.strict will print 'Hello anonymous' and throw an error when the callback will be called the second time
|
|
greet(null, once.strict(msg))
|
|
```
|