我不明白javascript中的函数返回 [英] I don't understand function return in javascript

问题描述

谁能解释为什么在函数中使用javascript return语句?什么时候以及为什么要使用它?

Can anyone explain why javascript return statement is used in function? when and why we should use it?

请帮助我.

推荐答案

为什么要在函数中使用它?

Why is it used in a function?

1.返回函数结果

return执行所说的操作-将 returns 返回一些值到 function调用程序

The return does what is says - it returns back some values to the function caller

function sum(num1, num2) {
  var result = number1 + number2

  return result
}

var result = sum(5, 6) // result now holds value '11'

2.停止执行功能

使用return的另一个原因是因为它还会中断该函数的执行-这意味着，如果您按下return，该函数就会停止运行任何紧随其后的代码.

Another reason that return is used is because it also breaks the execution of the function - that means that if you hit return, the function stops running any code that follows it.

function sum(num1, num2) {
  // if any of the 2 required arguments is missing, stop
  if (!num1 || !num1) {
    return
  }

  // and do not continue the following

  return number1 + number2
}

var result = sum(5) // sum() returned false because not all arguments were provided

---

为什么要使用它?

Why we should use it?

因为它允许您重用代码.

Because it allows you to reuse code.

例如，如果您正在编写一个进行几何计算的应用程序，则可能需要计算两个点之间的距离；这是一个常见的计算.

If for example you're writing an application that does geometric calculations, along the way you might need to calculate a distance between 2 points; which is a common calculation.

• 您是否会在每次需要时再次编写公式 ?
• 如果您的公式有误怎么办?您可以访问所有地点中的 公式写在哪里进行更改的代码?

• Would you write the formula again each time you need it?
• What if your formula was wrong? Would you visit all the places in the code where the formula was written to make the changes?

否-相反，您可以将其包装到函数中并让其返回结果-因此，您只需编写一次公式，即可在需要的地方重复使用它:

No - instead you would wrap it into a function and have it return back the result - so you write the formula once and you reuse it everywhere you want to:

function getLineDistance(x1, y1, x2, y2) {
  return Math.sqrt((Math.pow((x2 - x1), 2)) + (Math.pow(( y2 - y1), 2)))
}

var lineDistance1 = getLineDistance(5, 5, 10, 20); 
var lineDistance2 = getLineDistance(3, 5, 12, 24);

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