String, Array, Object manipulation methods<br>

<input id="myNum01" type=text value="This is a string" ><br> 
<span id="mySpan01">...</span><br>

<input type=button value=".toUpperCase()" onclick="{
    let myIn = document.getElementById('myNum01').value
    document.getElementById('mySpan01').innerHTML = myIn.toUpperCase()
}"><br>

<input type=button value=".split() makes and array" onclick="{
    let myIn = document.getElementById('myNum01').value
    document.getElementById('mySpan01').innerHTML = myIn.split('')
}"><br>

<input type=button value="Object.keys() returns array" onclick="{
    let myObject = {
        first: 10,
        second: 'Hello',
        third: true
    }
    let keyArray = Object.keys(myObject)
    document.getElementById('mySpan01').innerHTML = keyArray
}"><br>
let str = "  Hello World  ";

// Length
console.log(str.length);

// Trim spaces
console.log(str.trim());

// Replace text
console.log(str.replace("World", "JavaScript"));

// Split into array
console.log(str.trim().split(" "));

// Convert case
console.log(str.toUpperCase());
console.log(str.toLowerCase());

// Substring
console.log(str.substring(0, 5));

let sentence = "apple, banana, cherry";
let list = sentence.split(", ");
console.log(list);   // ["apple", "banana", "cherry"]