The use of Array.push() within an $http.get() function in AngularJs results in an array with unexpected

Question

The use of Array.push() within an $http.get() function in AngularJs results in an array with unexpected

I'm stuck trying to debug my code, particularly because it seems to be related to a javascript issue.

The problem arises when I attempt to load a local txt file using $http.get (is there another method that might work better?). The goal is to store this content in an array. To troubleshoot, I am currently just pushing a generic string into the array to rule out any issues with the actual txt file itself.

 var myArray = [];
 $http.get(localFilePath).then(
        function(success){
            myArray.push("123");
        },
        function(error){
            // other stuff
        });

console.log(myArray);

This basic code snippet does not seem to create the desired array format. When I use console.log to view the array in Chrome Dev Tools, it appears fine:

https://i.sstatic.net/NH8FS.png

Despite looking correct, the array actually fails to populate - console.log(myArray.length) always shows 0.

On the contrary, here's how an expected array should appear using the same syntax of myArray.push("123") but placed outside the $http.get() function:

https://i.sstatic.net/jxm4d.png

What exactly sets these two arrays apart and causes the first one to be structured differently when created within the $http.get() function?

javascript arrays angularjs http-get

Answer 1

Answer №1

The issue at hand is related to the asynchronous nature of the operation. The problem lies in calling console.log() outside of the promise's "resolve" function.

var myArray = []
$http.get(localFilePath).then(function(result) {
  myArray.push("123")
})

// code outside the resolve function     
console.log(myArray)

Because this operation is asynchronous, the resolve function is only executed once the $http.get() request has completed (which typically takes a few hundred milliseconds). Due to this, other parts of the code continue execution without waiting. This means that the get() function is triggered, followed immediately by the console.log(), before the http request finishes and populates the array.

If you were to move the console.log() inside the resolve function, you would observe that the array is correctly populated. This is because it waits for the http request to finish, updates the array, and then prints the result.

$http.get(localFilePath).then(function(result) {
  myArray.push("123")

  // code inside the resolve function     
  console.log(myArray)
})

Answer 2

The issue at hand is related to the asynchronous nature of the operation. The problem lies in calling console.log() outside of the promise's "resolve" function.

var myArray = []
$http.get(localFilePath).then(function(result) {
  myArray.push("123")
})

// code outside the resolve function     
console.log(myArray)

Because this operation is asynchronous, the resolve function is only executed once the $http.get() request has completed (which typically takes a few hundred milliseconds). Due to this, other parts of the code continue execution without waiting. This means that the get() function is triggered, followed immediately by the console.log(), before the http request finishes and populates the array.

If you were to move the console.log() inside the resolve function, you would observe that the array is correctly populated. This is because it waits for the http request to finish, updates the array, and then prints the result.

$http.get(localFilePath).then(function(result) {
  myArray.push("123")

  // code inside the resolve function     
  console.log(myArray)
})

Answer 3

Answer №2

When you use console.log before the array receives a value, the console in Chrome updates the array (as it's a reference type) but not the length (since it's a primitive type). This explains why you can see the length property properly set as part of the array.

If you try this code:

var myArray = [];
let $http = { get: () => {
    var p = new Promise((resolve, reject) => {
        setTimeout(() => resolve('hi'), 1000);
    })
    return p;
}}
$http.get('').then(
    function(success){
        myArray.push("123");
        console.log(myArray, myArray.length, 'after');
    },
    function(error){
        // other stuff
    }
);
console.log(myArray, myArray.length, 'before');

You will understand what I am trying to convey.

Answer 4

When you use console.log before the array receives a value, the console in Chrome updates the array (as it's a reference type) but not the length (since it's a primitive type). This explains why you can see the length property properly set as part of the array.

If you try this code:

var myArray = [];
let $http = { get: () => {
    var p = new Promise((resolve, reject) => {
        setTimeout(() => resolve('hi'), 1000);
    })
    return p;
}}
$http.get('').then(
    function(success){
        myArray.push("123");
        console.log(myArray, myArray.length, 'after');
    },
    function(error){
        // other stuff
    }
);
console.log(myArray, myArray.length, 'before');

You will understand what I am trying to convey.

Answer 5

Answer №3

I have reviewed your issue and tested the code provided. It seems that you are correctly pushing an object returned from the service into an array. The Array.push() method should work both inside and outside of the $http.get() service.

var myArray = [];
$http.get(localFilePath).then(
  function(success){
      myArray.push("123");
     return success
  },
  function(error){
      // handle errors
   return success
});

console.log(myArray);
var myArray2 = [];
myArray2.push("123");
console.log(myArray2);

Answer 6

I have reviewed your issue and tested the code provided. It seems that you are correctly pushing an object returned from the service into an array. The Array.push() method should work both inside and outside of the $http.get() service.

var myArray = [];
$http.get(localFilePath).then(
  function(success){
      myArray.push("123");
     return success
  },
  function(error){
      // handle errors
   return success
});

console.log(myArray);
var myArray2 = [];
myArray2.push("123");
console.log(myArray2);

The use of Array.push() within an $http.get() function in AngularJs results in an array with unexpected

Answer №1

Answer №2

Answer №3

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