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37 | 37 | |31|[Preventing paste into an input field](#Preventing-paste-into-an-input-field)| |
38 | 38 | |32|[The void operator](#The-void-operator)| |
39 | 39 | |33|[replaceAll](#replaceAll)| |
40 | | - |
| 40 | +|34|[Required Function Params](#Required-Function-Params)| |
41 | 41 |
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42 | 42 |
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43 | 43 | **[⬆ Back to Top](#table-of-contents)** |
@@ -711,6 +711,28 @@ const updatedStr = str.replaceAll('example', 'snippet'); //'this is a JSsnippets |
711 | 711 | ``` |
712 | 712 |
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713 | 713 |
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| 714 | +**[⬆ Back to Top](#table-of-contents)** |
| 715 | +### Required Function Params |
| 716 | +Expanding on the default parameter technique, we can mark a parameter as mandatory |
| 717 | +
|
| 718 | +```javascript |
| 719 | +const isRequired = () => { |
| 720 | + throw new Error( 'This is a mandatory parameter.' ); |
| 721 | +} |
| 722 | +
|
| 723 | +
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| 724 | +const getPage = ( pageName = 'Jssnippets', url = isRequired() ) => { |
| 725 | + return `${pageName} ${url}`; |
| 726 | +} |
| 727 | +
|
| 728 | +console.log(getPage()); |
| 729 | +
|
| 730 | +//In the above code, url will be undefined and that will try to set the default value for it which is the isRequired() function. It will throw an error as, |
| 731 | +
|
| 732 | +//Uncaught error: This is a mandatory parameter. |
| 733 | +//at isRequired |
| 734 | +
|
| 735 | +``` |
714 | 736 |
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715 | 737 |
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716 | 738 |
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