@tsdotnet/linq/dist/esm/resolutions/toMap.js

A familiar set of functions that operate on JavaScript iterables (ES2015+) in a similar way to .NET's LINQ does with enumerables.

import { ArgumentNullException } from '@tsdotnet/exceptions';
import identity from '../identity.js';

function toMap(keySelector, valueSelector = identity, mappingBehavior = -1) {
    if (!keySelector)
        throw new ArgumentNullException('keySelector');
    if (typeof valueSelector == 'number') {
        mappingBehavior = valueSelector;
        valueSelector = undefined;
    }
    if (!valueSelector)
        valueSelector = identity;
    return function (sequence) {
        const result = new Map();
        let i = 0;
        for (const e of sequence) {
            const key = keySelector(e, i++);
            if (result.has(key))
                switch (mappingBehavior) {
                    case 0:
                        continue;
                    case -1:
                        throw new Error('MappingMode.Throw: more than one of the same key encountered.');
                }
            result.set(key, valueSelector(e, i - 1));
        }
        return result;
    };
}

export { toMap as default };
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