String concatenation in JavaScript

We use the operator + to concatenate strings, as well as to add numbers:

javascriptlet str = 'abc' + 'def'; // add two strings
alert(str); // shows 'abcdef'

Strings can also be stored in variables:

javascriptlet str1 = 'abc';
let str2 = 'def';
alert(str1 + str2); // shows 'abcdef'

You can also add variables with strings:

javascriptlet str1 = 'abc';
let str2 = 'def';
alert(str1 + '!!!' + str2); // shows 'abc!!!def'

Let two strings are stored in variables, and we want to insert a space between them when we add them. It's done like this:

javascriptlet str1 = 'abc';
let str2 = 'def';
alert(str1 + ' ' + str2); // shows 'abc def'

Let there be only one variable:

javascriptlet str = 'abc';
alert(str + ' ' + 'def'); // shows 'abc def'

In this case, it makes no sense to arrange the space in the separate string - we will insert it as part of the second term:

javascriptlet str = 'abc';
alert(str + ' def'); // shows 'abc def'