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CYF array.map discussion
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| // We want to apply a function to each element of an array and get | |
| // back a new array of the same length, with a function applied to | |
| // each element. | |
| let arr = [1, 2, 3, 4, 5]; | |
| console.log(arr); | |
| // Then function takes one parameter (same type as the elements in | |
| // the array) and has to return something (or we end up with an | |
| // array of "undefined" values). | |
| function addOne(n) { | |
| return n+1; | |
| } | |
| // We can do it using a for loop | |
| let arr2 = []; | |
| for(i=0; i < arr.length; i++) { | |
| let newElement = addOne(arr[i]); | |
| arr2.push(newElement); | |
| } | |
| console.log(arr2); | |
| // But arr.map gives us the same result and is much simpler and | |
| // easier to read | |
| let arr3 = arr.map(addOne); | |
| console.log(arr3); | |
| // It works with strings too | |
| let names = ["Virginie", "Andy", "Tara"]; | |
| function upperCase(s) { | |
| return s.toUpperCase();; | |
| } | |
| console.log(names.map(upperCase)); | |
| // What's going on inside map is the same as our original for loop | |
| // version | |
| function myMap(f, someArray) { | |
| let arr2 = []; | |
| for(i=0; i < someArray.length; i++) { | |
| let newElement = f(someArray[i]); | |
| arr2.push(newElement); | |
| } | |
| return arr2; | |
| } | |
| let arr4 = myMap(addOne, arr); | |
| console.log(arr4); | |
| // The tricky thing is that we are passing a function as a parameter | |
| // to the function, rather than calling the function ourselves. map calls | |
| // the function for us. | |
| function doSomethingToANumber(f, n) { | |
| return f(n); | |
| } | |
| console.log(doSomethingToANumber(addOne, 2)); |
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