在Javascript中检查数组中元素的类型

Question

Just started with Javascript and am trying to check the type of an element in an array : I have a function that takes two functions as parameters . I have an array which has a combination of string and number elements. The idea is to trigger functions based on the type of element in the sample array and then push a new element to a new array . I'm not sure which bulit in function i can use here. I tried indexOf and typeof but these don't seem to serve the purpose or maybe I'm doing this wrong. Below is the code. Thanks a lot!

var arr1 = [3, "Hello", 5, "Hola"];

function setNewArray(arr, funct1, funct2){
    var arr2 = [];

    for(var i = 0; i < arr.length; i++){
        if(/*check if arr[i] is a string*/){
            arr2.push(funct1(arr[i]));
        }

        if(/*check if arr[i] is a number*/){
            arr2.push(funct2(arr[i]));
        }       
    }
    return arr2;
}


var numfunct = function(item){
    return item * 2;
}


var strfunct = function(item){
    return item + " " + "there";
}

var result = setNewArray(arr1, numfunct, strfunct);
console.log(result);

Answer 1

You can do it easily using typeof like following

For the first code block

if(typeof arr[i] === 'string'){
     arr2.push(   
     funct1(arr[i]));
}

For the second one

if(typeof arr[i] === 'number'){
      arr2.push(
      funct2(arr[i]));
    }   

Answer 2

Check this:

 var arr1 = [3, "Hello", 5, "Hola" ]; function setNewArray(arr, funct1, funct2){ var arr2 = []; for(var i = 0; i < arr.length; i++){ if(!isNaN(arr[i])){ // or use this alternative typeof arr[i] == 'number' arr2.push( funct1(arr[i])); } if(typeof (arr[i]) == 'string'){ arr2.push( funct2(arr[i])); } } return arr2; } var numfunct = function(item){ return item * 2; } var strfunct = function(item){ return item + " " + "there"; } var result = setNewArray(arr1, numfunct, strfunct); console.log(result); 

Answer 3

Create an object of functions, where each function name is the type it can handle. Iterate the array with Array#map , and select the right method from the object using typeof .

Note: I've added a boolean handler to convert the true to yes.

 var arr1 = [3, "Hello", 5, "Hola", true]; var fns = { number(item) { return item * 2; }, string(item) { return item + " " + "there"; }, boolean(item) { return item ? 'yes' : 'no' } }; function setNewArray(arr, fns) { return arr.map(function(item) { return fns[typeof item](item); }); } var result = setNewArray(arr1, fns); console.log(result); 

Answer 4

You can use typeof to check the type of any variable or object. And you do not need to pass the function refrence. Here is the code:

var arr1 = [3, "Hello", 5, "Hola"];

function setNewArray(arr) {
  var arr2 = [];

  for (var i = 0; i < arr.length; i++) {

    if (typeof arr[i] === 'string') {
      arr2.push(
        strfunct(arr[i]));
    }

    if (typeof arr[i] === 'number') {
      arr2.push(
        numfunct(arr[i]));
    }
  }
  return arr2;
}

var numfunct = function (item) {
  return item * 2;
}

var strfunct = function (item) {
  return item + " " + "there";
}

var result = setNewArray(arr1);
console.log(result);

Answer 5

Try using typeof Operator in javascript

 var arr1 = [3, "Hello", 5, "Hola"]; function setNewArray(arr, funct1, funct2) { var arr2 = []; for (var i = 0; i < arr.length; i++) { if (typeof arr[i] == 'string') { arr2.push(funct1(arr[i])); } if (typeof arr[i] == 'number') { arr2.push(funct2(arr[i])); } } return arr2; } var numfunct = function (item) { return item * 2; } var strfunct = function (item) { return item + " " + "there"; } var result = setNewArray(arr1, strfunct, numfunct); console.log(result); 

I think this is the exact function that you are looking for.

Answer 6

The problem was not with the use of typeof operator but with the function called with number and string.

Updated code:

var arr1 = [3, "Hello", 5, "Hola" ];

function setNewArray(arr, funct1, funct2){

    var arr2 = [];

    for(var i = 0; i < arr.length; i++){

        if(typeof arr[i] == "string"){
         arr2.push(   
            funct2(arr[i]));
        }


        if(typeof arr[i] == "number"){

          arr2.push(

              funct1(arr[i]));
        }       


    }
    return arr2;
    }


var numfunct = function(item){

    return item * 2;

}


var strfunct = function(item){

    return item + " " + "there";
}

var result = setNewArray(arr1, numfunct, strfunct);
console.log(result);