During my exploration of an Angular 4 tutorial, I stumbled upon a different approach to handling parameters in functions.
onValueChange(data?: any)
I am curious about the purpose and functionality of the ? symbol here. Can you explain its significance to me?
? symbol indicates that a parameter is optional in a function. This means that if you do not provide a value for the parameter, it will not result in an error.
For instance:
Consider this function:
onValueChange(data?: any) {
console.log(data);
}
onValueChange('somedata'); // will display 'somedata' in the console
onValueChange(); // will show 'undefined', but no error will be thrown
In summary: You have the flexibility to invoke this function without providing a value for the optional parameter.
This parameter is not required. We have the choice to include it or omit it without causing an error. The function can be invoked in two different ways as shown below:
onValueChange('somedata');
onValueChange();
Within the realm of JavaScript, each parameter is considered to be discretionary, allowing users the freedom to omit them at will. Should a parameter be excluded, its value defaults to undefined. This same flexibility can be achieved in TypeScript by appending a ? to designate which parameters are optional.
Essentially, this means that when handling bound value change events, users have the choice to either specify certain values upon occurrence or simply trigger the function without passing any specific arguments.
It describes the concept of being optional. After defining a function/method in this way, you have the choice to either provide a value or not.
onValueChange(data?: any) {} can be written as simply onValueChange() {} when the function is defined with onValueChange(data?: any) {}.
Similarly, when creating models, you can follow the same approach.
For instance:
export class YOURCLASS{
ids?: number[];
name :string
}
In this example, you may or may not include an ids array, but the name parameter must definitely be included.
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