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JavaScript: Extract the first half of a string of even length

JavaScript Basic: Exercise-59 with Solution

Write a JavaScript program to extract the first half of a string of even length.

Pictorial Presentation:

JavaScript:  Extract the first half of a string of even length

Sample Solution:

HTML Code:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JavaScript program to  extract the first half of a string of even length.</title>
</head>
<body>

</body>
</html>

JavaScript Code:

function first_half (str) {
  if (str.length % 2 == 0) {
    return str.slice(0, str.length / 2);
  }
  return str;
}
console.log(first_half("Python"));  
console.log(first_half("JavaScript")); 
console.log(first_half("PHP"));

Sample Output:

Pyt
JavaS
PHP

Flowchart:

Flowchart: JavaScript - Extract the first half of a string of even length

ES6 Version:

function first_half (str) {
  if (str.length % 2 == 0) {
    return str.slice(0, str.length / 2);
  }
  return str;
}
console.log(first_half("Python"));  
console.log(first_half("JavaScript")); 
console.log(first_half("PHP"));

Visualize JavaScript code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Live Demo:

See the Pen JavaScript - Extract the first half of a string of even length - basic-ex-59 by w3resource (@w3resource) on CodePen.


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Previous: Write a JavaScript program to create a new string of 4 copies of the last 3 characters of a given original string.
Next: Write a JavaScript program to create a new string without the first and last character of a given string.

What is the difficulty level of this exercise?



JavaScript: Tips of the Day

Promise object

const myPromise = () => Promise.resolve('I have resolved!');

function firstFunction() {
  myPromise().then(res => console.log(res));
  console.log('second');
}

async function secondFunction() {
  console.log(await myPromise());
  console.log('second');
}

firstFunction();
secondFunction();

With a promise, we basically say I want to execute this function, but I'll put it aside for now while it's running since this might take a while. Only when a certain value is resolved (or rejected), and when the call stack is empty, I want to use this value.
We can get this value with both .then and the await keyword in an async function. Although we can get a promise's value with both .then and await, they work a bit differently.
In the firstFunction, we (sort of) put the myPromise function aside while it was running, but continued running the other code, which is console.log('second') in this case. Then, the function resolved with the string I have resolved, which then got logged after it saw that the callstack was empty.
With the await keyword in secondFunction, we literally pause the execution of an async function until the value has been resolved before moving to the next line.
This means that it waited for the myPromise to resolve with the value I have resolved, and only once that happened, we moved to the next line: second got logged.

Ref: https://bit.ly/3jFRBje