9078a50a70
Adding markdown formatting for sections and more information on truthy. Also attempting to mirror how the falsy article is organized. Moving the conditional example from the bottom to the top of the file.
43 lines
1.7 KiB
Markdown
43 lines
1.7 KiB
Markdown
---
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title: Truthy Value
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---
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## Description
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A **truthy** value is a value that translates to **true** when evaluated in a _Boolean_ context.
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All values are **truthy** unless they are defined as **[falsy](https://github.com/freeCodeCamp/freeCodeCamp/blob/master/guide/english/javascript/falsy-values/index.md)** (i.e. except for `false`, `0`, `""`, `null`, `undefined` and `NaN`).
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## Checking for Truthy Values on Variables
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It is possible to check for a truthy value in a variable with a simple conditional:
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```javascript
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if (variable) {
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// When the variable has a truthy value the condition is true.
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}
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```
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You can also get the boolean value of a variable by using the bang operator (`!`) twice:
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```javascript
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!!variable // When the variable is truthy, a double bang (!!) will evaluate to the Boolean true.
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```
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### Interesting JavaScript Rules concerning Truthy Values
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#### These Are Interesting Truthy Values
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* '0' (a string containing a single zero)
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* 'false' (a string containing the text “false”)
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* [] (an empty array)
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* {} (an empty object)
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* function(){} (an “empty” function)
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#### Comparing Interesting Truthy Values
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* `false`, `zero` and `''`(empty strings) are all equivalent.
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* `null` and `undefined` are equivalent to themselves and each other but nothing else.
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* `NaN` is not equivalent to anything – including another `NaN!
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* `Infinity` is truthy – but cannot be compared to `true` or `false`!
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* An empty array(`[]`) is truthy – yet comparing with `true` is `false` and comparing with `false` is `true`?!
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## More Information
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See also: <a>falsy</a> | <a href='https://developer.mozilla.org/en-US/docs/Glossary/Truthy' target='_blank' rel='nofollow'>MDN</a>
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