Interview Q&A / JavaScript

61. Write your own version of Promise.all.

    Return a new promise. Keep a results array and a counter. Wrap each input in Promise.resolve, store its value at its index, and resolve when the counter reaches zero. Reject as soon as any input rejects.

    IntermediateQuick answerCoding1 min read
62. What is this after calling bind twice on the same function?

    The first bind wins. A bound function's this is permanent, so calling bind again on it, or call and apply, cannot change it. Only extra preset arguments from the second bind take effect.

    AdvancedQuick answer1 min read
63. Why does [] == ![] return true in JavaScript?

    ![] is false because an array is truthy. Then [] == false converts both sides to numbers: [] becomes "" then 0, and false becomes 0, so 0 == 0 is true.

    AdvancedQuick answer1 min read