Checking the type of an element in an array in Javascript

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);

Have a look at the documentation of typeof, parseFloat and parseInt. — Jeroen Heier
– Jeroen Heier, Commented Nov 1, 2017 at 5:00

PaulShovan · Accepted Answer · 2017-11-01 04:53:44Z

5

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]));
    }

answered Nov 1, 2017 at 4:53

PaulShovan

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2 Comments

PaulShovan Over a year ago

@Ben If you think this one solves your problem please mark it as an answer.

doubleOrt Over a year ago

Your code does not solve the problem because there is another problem with OP's code, they are passing the function for the number as func1 (same thing for the string function), and this is why I believe your question was not accepted.

Ori Drori · Accepted Answer · 2017-11-01 05:09:17Z

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);

doubleOrt · Accepted Answer · 2017-11-07 16:21:20Z

1

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);

edited Nov 7, 2017 at 16:21

doubleOrt

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answered Nov 1, 2017 at 4:56

ata

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5 Comments

doubleOrt Over a year ago

Why not just typeof arr[i] === "number" ? isNaN seems to provide only one advantage in this case, and that in an extremely unlikely case.

ata Over a year ago

@Taurus I edited my answer. I just wanted to use an alternative.

doubleOrt Over a year ago

I recommend editing it back then, that alternative was a bit different than the other solutions here, with this edit, your answer looks like a 1-to-1 clone of every other answer to this question.

ata Over a year ago

@Taurus how about both? :-)

doubleOrt Over a year ago

Nice but almost invisible :)

Nitheesh · Accepted Answer · 2017-11-01 04:55:41Z

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.

NishiJain · Accepted Answer · 2017-11-01 04:58:32Z

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);

Amit Singh · Accepted Answer · 2017-11-01 05:02:31Z

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);

Passing the functions as parameters makes the code more flexible.

VISHAL SINGH · Accepted Answer · 2024-07-11 04:03:50Z

0

the simple and easy trick to get an array type is the prototype: Object.prototype.isString.call(arr);

var arr = [1,2,3];
console.log(Object.prototype.isString.call(arr));

it will return you [object array]

answered Jul 11, 2024 at 4:03

VISHAL SINGH

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Comments

Prakash Ravichandran · Accepted Answer · 2024-10-19 08:37:59Z

You can make use of the below which i have refactored the code and that meets your output.

you just need only one funct utility that decides between the type of variable(str)
The isStringPrimitive() utility strongly check if it was created with '' literal(return true) or instead of new String() returns false;
use let instead of var because we are using (...)spread operator below.
use forEach loop makes more meaningful way of coding instead of native for(var i=0; condition; increment/decrement) syntax.
One funct uiltiy is sufficient -> var result = setNewArray(arr1,funct);

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

// you just need only one funct utility that decides between the type of variable(str)
const funct = function(item){
   return isStringPrimitive(item) ? item.concat(" ", "there") : item *2 ; 
  
} 

// this utility strong check if ut was create with '' literal(return true)  instead of new String() returns false;
const isStringPrimitive = (str) => {
  return typeof str === 'string' && !(str instanceof String);
}

// can utilize this if need 
const isNumberPrimitive = (str) => {
  return typeof str === 'number' && !(str instanceof Number);
}


function setNewArray(arr, funct1, funct2){
    // use let instead of var because we are using spread operator below
    let arr2 = []; 

    // use forEach loop makes more meaningful way of coding instead of native for(var i; ;) syntax
    arr.forEach((value) => {
      isStringPrimitive(value) ? arr2 = [ ...arr2, funct(value)]: arr2 = [ ...arr2, funct(value)];
    });
    
    return arr2;
}

var result = setNewArray(arr1,funct); // one funct uiltiy is sufficient
console.log(result); // [ 6, 'Hello there', 10, 'Hola there' ]

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