Console Learner — An interactive JavaScript course.

2.4 Statements

var a = 1;
var b = a + 1;

A ; character is used to separate statements. Several statements can be placed on a single line, although it is commonly avoided.
    var a = 1;
    a += 2;

The { and } characters are (also) used to group several statements. This is sometimes called a block.
a = 1, b = a + 1
The , operator in expressions is similar to the ; statement separator. It evaluates both expressions, but will only return the second one. Compare with the boolean operators:

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