javascript - 使用回调创建函数

Question

我试图通过解决这个问题来理解回调函数如何正常工作:

Complete the following merge function such that is behaves as described in the example below. Merge should take two arrays of numbers of identical length and a callback function.

var merge = function(array1, array2, callback){  
  //your code here.
}

var x = merge([1, 2, 3, 4], [5, 6, 7, 8], function(a, b){  
  return a + b;
});

//x should now equal [6, 8, 10, 12].

Now, use your merge function to complete the euclid function defined below. Euclid should take two arrays, each of which has an equal number of numerical elements, and return the euclidean distance between them. For a quick refresher on what Euclidean distance is, check here

var euclid = function(coords1, coords2){  
  //Your code here.
  //You should not use any loops and should
  //instead use your original merge function.
}

var x = euclid([1.2, 3.67], [2.0, 4.4]);

//x should now equal approximately 1.08.

我可以在没有回调的情况下完成此操作，但最终我想知道如何使用回调作为参数来完成这样的函数。

Answer 1

给你..

var merge = function(array1, array2, callback) {
  var result = [];
  if (array1.length === array2.length) {
    while (array1.length > 0) {
      result.push(callback.call(null, array1.shift(), array2.shift()));
    }
  }
  return result;
}

var euclid = function(coords1, coords2) {
  var x = merge(coords1, coords2, function(a, b) {
    return a - b;
  })
  return Math.sqrt(Math.pow(x[0], 2) + Math.pow(x[1], 2));
}

console.log(euclid([1.2, 3.67], [2.0, 4.4]));