Type Conversion with JavaScript Arrays

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JavaScript's loose nature allows developers to employ amazing tricks to do just about anything you'd like. I've detailed how you can filter falsy values in arrays using a filter(Boolean) trick, but reader David Hibshman shared another trick for typecasting array values the same way.

To typecast an array of elements, you can use map and the desired return type:

["1", "9", "-9", "0.003", "yes"].map(Number);
// [1, 9, -9, 0.003, NaN]

I love this trick but you could argue the code itself could be considered confusing, so wrapping it a helper function would be helpful:

function arrToNumber(arr) {
  return arr.map(Number).filter(Boolean);
}

Validation could and should probably be more rigorous but basic validation through typecasting might help you!

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Discussion

  1. jzrskc
    ["0", "9", "-9", "0.003", "yes", true, false, undefined, null].map(Number);
    // [0, 9, -9, 0.003, NaN, 1, 0, NaN, 0]
    
    ["0", "9", "-9", "0.003", "yes", true, false, undefined, null].map(parseFloat)
    // [0, 9, -9, 0.003, NaN, NaN, NaN, NaN, NaN]
    
  2. MKM

    The .filter(Boolean) part also sees the zeros as booleans and removes those numbers.

  3. BryanYang

    very useful!

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