My issue lies not with optional primitive parameters, but with optional functions. For example, say I have a function that requires one parameter and one optional parameter.
function performTask(input: string, callback?: () => void){
let temp = input;
callback(); // using callback!() also does not work
}
performTask('example') // this line triggers an error 'callback is not a function'
If you utilize the post bang in this manner:
callback!();
You are essentially asserting that, at this specific moment during the code interpretation process, callback will be present regardless of whether it is an optional value. As a result, the typescript compiler interprets it as something like this:
doSomething('test', undefined)
This misconception occurs because you have informed it that callback will indeed exist.
The correct approach is to manually verify the existence of the value:
if(callback){
callback();
}
By following this method, you can avoid any potential errors.
To ensure proper execution, it is important to verify if the callback function was passed:
function performTask(value: string, onCompletion?: () => void){
if (onCompletion !== undefined) {
onCompletion();
}
}
If this approach suits your needs, you can also utilize a default parameter.
function performTask(value: string, onCompletion: () => void = () => {}){
onCompletion();
}
Experiment with this code snippet:
let example = function (x, y = () => { console.log('default') }) {
y()
}
example(1);
example(()=>{console.log('provided')})
By utilizing = in the function parameter definition, you can avoid using ?
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