How do you explain this behavior of the map function?

• 0
  little experience in js. And the question is most likely stupid, but still did not find information about this.
  

  let cord = [{x: 0, y: 0, type: 5, active: true}]
  console.log(cord)
  //x=5
  cord.map(elem => elem.x = 5)
  
  console.log(cord)
  //x=5

  
  as far as I know, map produces a new array, the variable of which needs to be equated

  JavaScript Molly Rowe, Feb 12, 2020

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3 Answers
• 0
  In this case, the anonymous function in map changes the property x directly in the object - an array element that is passed to it by reference.
  
  The map function also has a result, it is [5].

  Anonymous

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• 0

  const cord = [{x: 0, y: 0, type: 5, active: true}]
  
  console.log(cord) // x = 0
  
  const newCoord = cord.map(elem => ({
  
  	...elem,
  
  	x: 5
  
  }))
  
  console.log(cord) // x = 0
  
  console.log(newCoord) // x = 5

  Milo Riggs

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• 0
  In your case, something like this happens:
  
  

  function incrementX(obj) {
  
    obj.x += 1
  
    return obj
  
  }
  
  
  
  var a = {x: 0}
  
  var b = incrementX(a)
  
  
  
  console.log(b) // {x: 1}
  
  console.log(a) // {x: 1} -- Магия

  
  
  
  
  Objects in JS are passed by reference. That is, passing an object as an argument to a function, the latter can modify it, which can lead to undesirable effects.

  Anonymous

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