How to print key and values from dictionaries enlisted in array, javascript - Stack Overflow

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I am having difficulties printing data from dictionaries stored in an array using double for-loop with

var residents = [{name: "Pyrus", room: "32"},{name: "Ash Ketchum", room: "22"}];

function people() {
    for (let i = 0; i < residents.length; i++) {
        for (let j in residents[i]) {
            document.write(j + ": " + residents[j] + "<br>");
        }
    }
};

people();

What I am retrieving is this:

name: undefined 
room: undefined
name: undefined
room: undefined

I can print the key but it seems like it does not fetch value defined to the key! What am I doing wrong?

A success criteria is to print in HTML.

I am having difficulties printing data from dictionaries stored in an array using double for-loop with

var residents = [{name: "Pyrus", room: "32"},{name: "Ash Ketchum", room: "22"}];

function people() {
    for (let i = 0; i < residents.length; i++) {
        for (let j in residents[i]) {
            document.write(j + ": " + residents[j] + "<br>");
        }
    }
};

people();

What I am retrieving is this:

name: undefined 
room: undefined
name: undefined
room: undefined

I can print the key but it seems like it does not fetch value defined to the key! What am I doing wrong?

A success criteria is to print in HTML.

• javascript
• arrays
• dictionary
• printing

Share Improve this question Follow asked Jul 30, 2018 at 15:49 DisabledWhaleDisabledWhale 87111 gold badge1010 silver badges1515 bronze badges 1

• 3 should be residents[i][j] – mhodges Commented Jul 30, 2018 at 15:55

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6 Answers 6

Sorted by: Reset to default 2

You have chained two loops together so your function needs to access the parents index then the property that you wish to reference.

function people() {
    for (let i = 0; i < residents.length; i++) {
        for (let j in residents[i]) {
            document.write(j + ": " + residents[i][j] + "<br>");
        }
    }
};

This is the simplest way I think(Use foreach()):

var residents = [{name: "Pyrus", room: "32"},{name: "Ash Ketchum", room: "22"}];

function people() {
    residents.forEach(function(resident) {
 document.write(resident.name + ": " + resident.room + "<br>");
});

}
people();

why not try like this with forEach()

var residents = [{
  name: "Pyrus",
  room: "32"
}, {
  name: "Ash Ketchum",
  room: "22"
}];

function people(residents) {
  residents.forEach((element) => {
    for (var key in element) {
      if (element.hasOwnProperty(key)) {
        console.log(key + ':' + element[key]);
      }
    }
  });

};
people(residents);

You can avoid some of the for loops and make the code a little easier to read using forEach and Object.entries:

var residents = [{name: "Pyrus", room: "32"},{name: "Ash Ketchum", room: "22"}];

residents.forEach(res => {
    Object.entries(res).forEach(([key, value]) => {
    console.log(key + ": " + value ); //subing console.log so it prints here
    //document.write(key + ": " + value + "<br>");
    })
})

Using a regular for-loop it would go like the below code. Also, I strongly remend you to check if all the properties (j) are own properties (with hasOwnProperty), otherwise this will look up in the prototype chain. This can be a problem if the objects are added to the array dynamically, otherwise you can bypass this check.

var residents = [{name:"Pyrus",room:"32"},{name: "Ash Ketchum",room:"22"}];

function people() {
  for (let i = 0; i < residents.length; i++) {
    for (let j in residents[i]) {
      if (residents[i].hasOwnProperty(j)) { // <-- check if it is an own property!
        document.write(j + ": " + residents[i][j] + "<br>");
        //first access the object in residents[i], for example {name: "Pyrus",room: "32"}, then to its properties-values with residents[i][j]
      }
    }
  }
};

people();

You need to access residents[i][j] since you are iterating residents in the first place.

so your code bees :

document.write(j + ": " + residents[i][j] + "<br>");

See this working js fiddle

You could also write it like this :

function people(){
    residents.forEach(r => {
        for(let j in r){
          document.write(j + ": " + r[j] + "<br>");
      }
    })
}

Hope this helps.

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