Why does this JavaScript Array from object returning wrong?

Why does this JavaScript Array from object returning wrong length. The JavaScript code creates array from array-like using length. In JavaScript a malicious length can allocate huge or wrong size.

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https://www.youtube.com/watch?v=RXjQ1w5hEeg

Why does this JavaScript Array from object returning wrong? #whatswrongwiththisjavascriptcode

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What's wrong with this JavaScript Map for object keys?

What's wrong with this JavaScript Map for object keys with reference equality. The JavaScript code uses objects as Map keys. In JavaScript key lookup uses reference so same-shaped objects do not match.

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https://www.youtube.com/watch?v=XPMqdgpMOqY

Whats wrong with this JavaScript Map for object keys? #whatswrongwiththisjavascriptcode

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Why does this JavaScript indexOf with NaN always returns -1?

Why does this JavaScript indexOf with NaN always returns -1. The JavaScript code uses indexOf to find a calculation result. In JavaScript indexOf uses strict equality and NaN never equals itself.

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https://www.youtube.com/watch?v=oTpEC9kdh0s

Why does this JavaScript indexOf with NaN always returns -1? #javascriptengineering

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Why does this JavaScript Promise.all lose writes?

Why does this JavaScript Promise.all lose writes in a fan out job. The JavaScript code allows one rejection to cancel all other promises. In JavaScript pipelines this causes partial writes and missing data.

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https://www.youtube.com/watch?v=aiDfylWMe9Y

Why does this JavaScript Promise.all lose writes? #javascriptperformance

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