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This is a playground to test code. It runs a full Node.js environment and already has all of npm’s 1,000,000+ packages pre-installed, including @extra-lists/union-keys.min. Try it out:
const lists = require('extra-lists');
var x = [['a', 'b', 'c', 'd'], [1, 2, 3, 4]];
var y = [['b', 'c', 'e'], [20, 30, 50]];
lists.unionKeys(x, y);
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