Concatenate

Furthermore, you can concatenate different conditions with "or" or “and” statements, to test whether either statement is true, or both are true, respectively.

In JavaScript “or” is written as || and “and” is written as &&.

Say you want to test if the value of x is between 10 and 20. You could do that with a condition stating:

if (x > 10 && x < 20) {
    ...
}

If you want to make sure that country is either “England” or “Germany” you use:

if (country === "England" || country === "Germany") {
    ...
}

Note: Just like operations on numbers, conditions can be grouped using parenthesis, ex: if ( (name === "John" || name === "Jennifer") && country === "France").