The if construct specifies a
condition. Using this construct,
we can ask the program,
for example, the question "is the
variable a greater than the variable
b", and depending on the answer,
execute one code or another.
As a rule, this construct is used in
combination with the
else
construct.
Syntax
if (logical expression) {
/*
a code located here will be executed
if the logical expression is true
*/
};
If there is only one expression in curly braces, these curly braces can be omitted.
Example
If the variable value is equal to one, we will display some message on the screen:
let test = 1;
if (test == 1) {
alert('+++');
}
Example
Let's check if the variable value is greater than zero or not:
let test = 1;
if (test > 0) {
alert('+++');
} else {
alert('---');
}
Example
The if-else constructs can
be nested in each other in an
arbitrary way:
let num = 3;
if (num >= 0) {
if (num <= 5) {
alert('less than or equal to 5');
} else {
alert('greater than 5');
}
} else {
alert('less than zero');
}