CODEWITHSUNDEEP
javascriptarraystypeselement
Ben
Ben

Reputation: 21

Checking the type of an element in an array in Javascript

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);

Upvotes: 2

Views: 21614

Answers (8)

Prakash Ravichandran
Prakash Ravichandran

Reputation: 3

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

  1. you just need only one funct utility that decides between the type of variable(str)
  2. The isStringPrimitive() utility strongly check if it was created with '' literal(return true) or instead of new String() returns false;
  3. use let instead of var because we are using (...)spread operator below.
  4. use forEach loop makes more meaningful way of coding instead of native for(var i=0; condition; increment/decrement) syntax.
  5. 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' ]

Upvotes: 0

VISHAL SINGH
VISHAL SINGH

Reputation: 661

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]

Upvotes: 0

ata
ata

Reputation: 3640

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);

Upvotes: 1

Ori Drori
Ori Drori

Reputation: 191976

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);

Upvotes: 1

Amit Singh
Amit Singh

Reputation: 436

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);

Here is the output

Upvotes: 0

NishiJain
NishiJain

Reputation: 121

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);

Upvotes: 0

Nitheesh
Nitheesh

Reputation: 19986

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.

Upvotes: 0

PaulShovan
PaulShovan

Reputation: 2134

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]));
    }

Upvotes: 5

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