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musix-oss/node_modules/date-and-time/EXTEND.md
2020-03-03 22:30:50 +02:00

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# Extension
By using `extend()`, you could add your own tokens or modify behavior of existing tokens. This is equivalent to define a new plugin without name.
## Token
Tokens in this library have the following rules:
- All of the characters must be the same alphabet (`A-Z, a-z`).
```javascript
'E' // Good
'EE' // Good
'EEEEEEEEEE' // Good, but why so long!?
'EES' // Not good
'???' // Not good
```
- It is case sensitive.
```javascript
'eee' // Good
'Eee' // Not good
```
- To the parser, it is not able to add token of new alphabet.
```javascript
'EEE' // This is not able to add because `E` is not an existing token in the parser.
'YYY' // This is OK because `Y` token is existing in the parser.
'SSS' // This is modifying, not adding. Because exactly the same token is existing.
```
## Examples
### Example 1
Add `E` token to the formatter. This new token will output "decade" like this:
```javascript
const d1 = new Date(2020, 0, 1);
const d2 = new Date(2019, 0, 1);
date.format(d1, '[The year] YYYY [is] E[s].'); // => "The year 2020 is 2020s."
date.format(d2, '[The year] YYYY [is] E[s].'); // => "The year 2019 is 2010s."
```
Source code example is here:
```javascript
const date = require('date-and-time');
date.extend({
formatter: {
E: function (d) {
return (d.getFullYear() / 10 | 0) * 10;
}
}
});
```
### Example 2
In the parser, modify `MMM` token to ignore case:
```javascript
date.parse('Dec 25 2019', 'MMM DD YYYY'); // => December 25, 2019
date.parse('dec 25 2019', 'MMM DD YYYY'); // => December 25, 2019
date.parse('DEC 25 2019', 'MMM DD YYYY'); // => December 25, 2019
```
Source code example is here:
```javascript
const date = require('date-and-time');
date.extend({
parser: {
MMM: function (str) {
const mmm = this.res.MMM.map(m => m.toLowerCase());
const result = this.find(mmm, str.toLowerCase());
result.value++;
return result;
}
}
});
```
Modifying the parser may be a bit difficult. Refer to the library source code to grasp the default behavior.