Javascript Fetch Api

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Developers often need to retrieve data from their own API or a third-party API. This article talks about using the browser Fetch API to GET data from an endpoint.

The Fetch API is an interface that allows us to send HTTP requests to a server from a web browser such as Chrome or Firefox. A GET request reaches an endpoint on a server and then returns a response with data from that endpoint so that you can read it.

Types of requests

The HTTP GET request is just one type of request you can make to a server. The other types of requests are POST, PUT, and DELETE. These requests make a CRUD request. This is where we can create (POST), read (GET), update (PUT) and destroy (DELETE) the data in our database.

In addition, we can access third party APIs ends. According to the API, you will only be allowed to run certain queries, mainly to keep their data immutable, so you won’t be able to run those queries that manipulate the data, you will only be able to read them.

How does the Fetch API work ?

The Fetch API uses a Promise-based communication system. As a reminder, promises are asynchronous functions that wrap logic in their own block of code and return a response that determines whether the promise has been resolved or rejected.

As a user of the Fetch API, you don’t expose us There is no need to actually write the logic of the promise. Just use it to send a request and the Fetch API returns a hidden promise. Here is the basic syntax for you to get the answer:

promise.then (response) .then (json) .catch (error) ;

The promise is the asynchronous request The fetch () method is available in global scope and passed to the endpoint we want to do the HTTP request.

After the request, we can use the syntax promised with then and catch or use the async / wait function to get the response from the server.

Promise syntax

Here we take the promise and wait for a response. When we get a response, if the status code is different from 200, we log an error code on our console and terminate the function.

Otherwise, to make the response readable so that our frontend website can use it, we change it to a JavaScript Object Notation (JSON) object with the json () . We want this to be evaluated before we move forward, so let’s chain a promise to the previous promise.

Once evaluated, we can record what has been spent to see it on our console. If you follow you should get something like this:

If we get this information on the frontend, we can use it to fill out cards or table or otherwise we would like to display it.

Async / Await

You can also use the async / wait function to save the same result.

The keyword async tells us that ’part of this function will be asynchronous. When we get to the wait keyword, script execution stops until this line of code is evaluated.

We have two wait statements in this function, comparable to the two then () statements we had in the promise logic. a to the url we browsed and the other until the fetched information is parsed into JSON. We use try / catch to catch errors that might occur if something unusual comes back from the responses.

Endnotes

In order for the Fetch API to work in node environment (i.e. if you are using an IDE like Visual Studio Code) you will need wire add or npm install node-fetch, because fetch only works in the browser environment.

Javascript Fetch Api __del__: Questions

How can I make a time delay in Python?

5 answers

I would like to know how to put a time delay in a Python script.

2973

Answer #1

import time
time.sleep(5)   # Delays for 5 seconds. You can also use a float value.

Here is another example where something is run approximately once a minute:

import time
while True:
    print("This prints once a minute.")
    time.sleep(60) # Delay for 1 minute (60 seconds).

2973

Answer #2

You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

from time import sleep
sleep(0.1) # Time in seconds

How to delete a file or folder in Python?

5 answers

How do I delete a file or folder in Python?

2639

Answer #1


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

Javascript Fetch Api __delete__: Questions

2639

Answer #2


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

2639

Answer #3

Python syntax to delete a file

import os
os.remove("/tmp/<file_name>.txt")

Or

import os
os.unlink("/tmp/<file_name>.txt")

Or

pathlib Library for Python version >= 3.4

file_to_rem = pathlib.Path("/tmp/<file_name>.txt")
file_to_rem.unlink()

Path.unlink(missing_ok=False)

Unlink method used to remove the file or the symbolik link.

If missing_ok is false (the default), FileNotFoundError is raised if the path does not exist.
If missing_ok is true, FileNotFoundError exceptions will be ignored (same behavior as the POSIX rm -f command).
Changed in version 3.8: The missing_ok parameter was added.

Best practice

  1. First, check whether the file or folder exists or not then only delete that file. This can be achieved in two ways :
    a. os.path.isfile("/path/to/file")
    b. Use exception handling.

EXAMPLE for os.path.isfile

#!/usr/bin/python
import os
myfile="/tmp/foo.txt"

## If file exists, delete it ##
if os.path.isfile(myfile):
    os.remove(myfile)
else:    ## Show an error ##
    print("Error: %s file not found" % myfile)

Exception Handling

#!/usr/bin/python
import os

## Get input ##
myfile= raw_input("Enter file name to delete: ")

## Try to delete the file ##
try:
    os.remove(myfile)
except OSError as e:  ## if failed, report it back to the user ##
    print ("Error: %s - %s." % (e.filename, e.strerror))

RESPECTIVE OUTPUT

Enter file name to delete : demo.txt
Error: demo.txt - No such file or directory.

Enter file name to delete : rrr.txt
Error: rrr.txt - Operation not permitted.

Enter file name to delete : foo.txt

Python syntax to delete a folder

shutil.rmtree()

Example for shutil.rmtree()

#!/usr/bin/python
import os
import sys
import shutil

# Get directory name
mydir= raw_input("Enter directory name: ")

## Try to remove tree; if failed show an error using try...except on screen
try:
    shutil.rmtree(mydir)
except OSError as e:
    print ("Error: %s - %s." % (e.filename, e.strerror))

Is there a simple way to delete a list element by value?

5 answers

I want to remove a value from a list if it exists in the list (which it may not).

a = [1, 2, 3, 4]
b = a.index(6)

del a[b]
print(a)

The above case (in which it does not exist) shows the following error:

Traceback (most recent call last):
  File "D:zjm_codea.py", line 6, in <module>
    b = a.index(6)
ValueError: list.index(x): x not in list

So I have to do this:

a = [1, 2, 3, 4]

try:
    b = a.index(6)
    del a[b]
except:
    pass

print(a)

But is there not a simpler way to do this?

1055

Answer #1

To remove an element"s first occurrence in a list, simply use list.remove:

>>> a = ["a", "b", "c", "d"]
>>> a.remove("b")
>>> print(a)
["a", "c", "d"]

Mind that it does not remove all occurrences of your element. Use a list comprehension for that.

>>> a = [10, 20, 30, 40, 20, 30, 40, 20, 70, 20]
>>> a = [x for x in a if x != 20]
>>> print(a)
[10, 30, 40, 30, 40, 70]

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