CODEWITHSUNDEEP
javascriptreactjsasynchronousreact-nativeecmascript-6
Maiko Francisco Rugeria
Maiko Francisco Rugeria

Reputation: 107

Understanding React Native Program Flow - Loops

[EDIT BELOW]

Here is the current code:

for(toy of toys) {
    fetch(url, {headers: headers})
       .then((response) => response.json)
       .then((responseJson) => {
           <insert toy to database>
       })
}

The code above does not post toy properly because the loop completes before the fetch inside does. How do I implement this properly so that I can insert toys with responseJson properties to the database properly? In other words, how can I wait for the fetch to complete before proceeding with the loop?

[PREVIOUS POST]

I have the following code:

function hello(callback1) {
   for(var i = 0; i <= 100; i++){
       console.log(i)
   }

   callback1()
}

function callback1() {
   console.log("hello")
}

My question is, will callback1 wait for the loop to finish or not?

Here is a second scenario:

function hello() {
   for(var i = 0; i < 100; i++){
      console.log("apples")
   }

   for(var i = 0; i < 100; i++){
      console.log("peaches")
   }
}

Will the output be:

apples
apples
apples
apples
...
peaches
peaches
peaches
...

or

apples
apples
peaches
apples
peaches
...(in any order since they execute at the same time)

I'm having a hard time understanding the flow of react native programs as I am used to linear execution of codes. If you can also suggest readings for dummies, that would be great.

Upvotes: 0

Views: 371

Answers (2)

Maiko Francisco Rugeria
Maiko Francisco Rugeria

Reputation: 107

I found the answer in this post:

How to make a javascript FOR LOOP wait for certain conditions before looping

In these situations, recursion is more appropriate to use.

Upvotes: 0

Erazihel
Erazihel

Reputation: 7605

As mention in the MDN documentation, the syntax of a for loop is:

for ([initialization]; [condition]; [final-expression])
    statement

Where statement is:

A statement that is executed as long as the condition evaluates to true. To execute multiple statements within the loop, use a block statement ({ ... }) to group those statements. To execute no statement within the loop, use an empty statement (;).

This means that everything in the for loop will be executed before executing the following code.

function hello(callback1) {
   for(var i = 0; i <= 10; i++){
       console.log(i)
   }

   callback1()
}

function callback1() {
   console.log("hello")
}

hello(callback1);

Upvotes: 1

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