Check if – Javascript
Hi, in this post we are going to see the result of some comparisons when we use an “If & else”
Checking empty string
const name = ""; // "" is Falsy or "cristina" is Truthy
if (name) {
console.log("enter if --> true");
} else {
console.log("enter else ---> false");
}
Result:
Checking null value
const name = null; // null is Falsy
if (name) {
console.log("enter if --> true");
} else {
console.log("enter else ---> false");
}
Result:
Or we can do this:
const name = null; // null is Falsy
if (!name) { // if null is falsy
console.log("enter if --> true");
}
Result:
Checking undefined
const name = undefined; // undefined is Falsy
if (name) {
console.log("enter if --> true");
} else {
console.log("enter else ---> false");
}
Result:
The undefined is a variable that has been declared but not assigned a value
let name; // name is undefined because undefined is a variable that has been declared but not assigned a value
if (name === undefined) {
console.log("enter if --> true");
}
if (typeof name === "undefined") {
console.log("enter if --> true");
}
Result:
Note: Don’t be confuse null
is an object but the type of undefined
is undefined.
We can evaluate if is false or true
// evaluates to false because name === undefined
let name; // name is undefined
if (name) { // undefined is true?
console.log("enter if --> true");
}
We can do this:
let name; // name is undefined and udefined is falsy
if (!name) { // if name is falsy
console.log("enter if --> true");
}
Result:
By Cristina Rojas.