Anything left of the assignment operator (=), as well as any expression that has no assignment operator is considered a left hand side expression.
MemberExpression :
PrimaryExpression
FunctionExpression
MemberExpression [ Expression ]
MemberExpression . IdentifierName
new MemberExpression Arguments
NewExpression :
MemberExpression
new NewExpression
CallExpression :
MemberExpression Arguments
CallExpression Arguments
CallExpression [ Expression ]
CallExpression . IdentifierName
Arguments :
( )
( ArgumentList )
ArgumentList :
AssignmentExpression
ArgumentList , AssignmentExpression
LeftHandSideExpression :
NewExpression
CallExpression
Interesting to note is that any property access is a CallExpression (but not actually a call... except perhaps to a getter :)). The exact evaluation is explained in the following paragraphs.