Consider the following function
``` js
/**
* Parses the locale sensitive string [value] into a number.
*/
export function parseNumber(
value: string,
locale: string = navigator.language
): number {
let decimalSeparator = decimalSeparators.get(locale);
if (!decimalSeparator) {
decimalSeparator = Intl.NumberFormat(locale).format(1.1)[1];
decimalSeparators.set(locale, decimalSeparator);
}
let cleanRegExp = regExps.get(decimalSeparator);
if (!cleanRegExp) {
cleanRegExp = new RegExp(`[^-+0-9${decimalSeparator}]`, 'g');
regExps.set(decimalSeparator, cleanRegExp);
}
value = value
.replace(cleanRegExp, '')
.replace(decimalSeparator, '.');
return parseFloat(value);
}
const decimalSeparators = new Map<string, string>();
const regExps = new Map<string, RegExp>();
```
This function can be simplified quite a bit as follows
``` js
export function parseNumber(
value: string,
locale: string = navigator.language
): number {
const decimalSeparator = decimalSeparators.putIfAbsent(
locale, () => Intl.NumberFormat(locale).format(1.1)[1]);
const cleanRegExp = regExps.putIfAbsent(
decimalSeparator, () => new RegExp(`[^-+0-9${decimalSeparator}]`, 'g'));
value = value
.replace(cleanRegExp, '')
.replace(decimalSeparator, '.');
return parseFloat(value);
}
```
if `Map` has the following instance method
``` js
export class Map<K, V> {
/**
* Look up the value of [key], or add a new value if it isn't there.
*
* Returns the value associated to [key], if there is one.
* Otherwise calls [ifAbsent] to get a new value, associates [key] to
* that value, and then returns the new value.
*/
putIfAbsent(key: K, ifAbsent: () => V): V {
let v = this.get(key);
if (v === undefined) {
v = ifAbsent();
this.set(key, v);
}
return v;
}
}
```
Java's Map has a `putIfAbsent` method, which accepts a value rather than a
function for the second parameter. This is not ideal as computing the value may
be expensive. A function would allow the value to be computed lazily.
References
- [Dart]
[Map.putIfAbsent](https://api.dartlang.org/stable/2.0.0/dart-core/Map/putIfAbsent.html)
- [Java]
[Map.putIfAbsent](https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#putIfAbsent-K-V-)
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