different solutions to check for duplicates

simple.js

const hasDuplicateOneline = (array) => 
    new Set(array).size != array.length;

const hasDuplicateAlternative = (arr) =>
     arr.some((value, index, origin) => origin.indexOf(value) !== index);

let z = [];
for (let i = 0; i < 10_000; i++) {
    z.push(i);
}
// z.push(1);

const testFunctions = [hasDuplicateOneline, hasDuplicateAlternative];
let start, stop, avg, execTime = {};

for (let index in testFunctions) {
    const func = testFunctions[index];
    execTime[func.name] = [];
    for (let j=0; j<1000; j++) {
        
        performance.mark('start');
        testFunctions[index](z);

        performance.mark('stop');
        performance.measure('executionTime', 'start', 'stop');
        execTime[func.name].push(performance.getEntriesByName('executionTime')[0].duration);
    }
    performance.clearMarks();
    performance.clearMeasures();
}

console.log(`${z.length} elements:`);
for (let index in testFunctions) {
    const func = testFunctions[index];
    avg = execTime[func.name].reduce((prev, cur) => {return prev + cur}, 0) / execTime[func.name].length;
    console.log(`${func.name} ${execTime[func.name].length} runs avg: ${avg}`);
}

Set has size property, not length. The current version

const hasDuplicateOneline = (array) => 
    new Set(array).length != array.length;

is evaluating undefined != array.length.

That is currently

hasDuplicateOneline([1,2,3]) // true

evaluates to true, which is incorrect.

Should be

var hasDuplicateOneline = (array) => 
    new Set(array).size != array.length;

hasDuplicateOneline([1,2,3]) // false

well pointed, I updated the code. Yet the difference is still noticeable

$ node simple.js
10000 elements:
hasDuplicateOneline 1000 runs avg: 0.6117080000000104
hasDuplicateAlternative 1000 runs avg: 10.793499999999812