docs/libs/typescript.js
function parseIncrementExpression() {
            if (token() === 41 /* PlusPlusToken */ || token() === 42 /* MinusMinusToken */) {
                var node = createNode(185 /* PrefixUnaryExpression */);
                node.operator = token();
                nextToken();
                node.operand = parseLeftHandSideExpressionOrHigher();
                return finishNode(node);
            }
            else if (sourceFile.languageVariant === 1 /* JSX */ && token() === 25 /* LessThanToken */ && lookAhead(nextTokenIsIdentifierOrKeyword)) {
                // JSXElement is part of primaryExpression
                return parseJsxElementOrSelfClosingElement(/*inExpressionContext*/ true);
            }
            var expression = parseLeftHandSideExpressionOrHigher();
            ts.Debug.assert(ts.isLeftHandSideExpression(expression));
            if ((token() === 41 /* PlusPlusToken */ || token() === 42 /* MinusMinusToken */) && !scanner.hasPrecedingLineBreak()) {
                var node = createNode(186 /* PostfixUnaryExpression */, expression.pos);
                node.operand = expression;
                node.operator = token();
                nextToken();
                return finishNode(node);
            }
            return expression;
        }
function parseIncrementExpression() {
            if (token() === 41 /* PlusPlusToken */ || token() === 42 /* MinusMinusToken */) {
                var node = createNode(185 /* PrefixUnaryExpression */);
                node.operator = token();
                nextToken();
                node.operand = parseLeftHandSideExpressionOrHigher();
                return finishNode(node);
            }
            else if (sourceFile.languageVariant === 1 /* JSX */ && token() === 25 /* LessThanToken */ && lookAhead(nextTokenIsIdentifierOrKeyword)) {
                // JSXElement is part of primaryExpression
                return parseJsxElementOrSelfClosingElement(/*inExpressionContext*/ true);
            }
            var expression = parseLeftHandSideExpressionOrHigher();
            ts.Debug.assert(ts.isLeftHandSideExpression(expression));
            if ((token() === 41 /* PlusPlusToken */ || token() === 42 /* MinusMinusToken */) && !scanner.hasPrecedingLineBreak()) {
                var node = createNode(186 /* PostfixUnaryExpression */, expression.pos);
                node.operand = expression;
                node.operator = token();
                nextToken();
                return finishNode(node);
            }
            return expression;
        }
function parseIncrementExpression ( ) { if ( token ( ) === 41 /* PlusPlusToken */ || token ( ) === 42 /* MinusMinusToken */ ) { var node = createNode ( 185 /* PrefixUnaryExpression */ ) ; node . operator = token ( ) ; nextToken ( ) ; node . operand = parseLeftHandSideExpressionOrHigher ( ) ; return finishNode ( node ) ; } else if ( sourceFile . languageVariant === 1 /* JSX */ && token ( ) === 25 /* LessThanToken */ && lookAhead ( nextTokenIsIdentifierOrKeyword ) ) { // JSXElement is part of primaryExpression return parseJsxElementOrSelfClosingElement ( /*inExpressionContext*/ true ) ; } var expression = parseLeftHandSideExpressionOrHigher ( ) ; ts . Debug . assert ( ts . isLeftHandSideExpression ( expression ) ) ; if ( ( token ( ) === 41 /* PlusPlusToken */ || token ( ) === 42 /* MinusMinusToken */ ) && ! scanner . hasPrecedingLineBreak ( ) ) { var node = createNode ( 186 /* PostfixUnaryExpression */ , expression . pos ) ; node . operand = expression ; node . operator = token ( ) ; nextToken ( ) ; return finishNode ( node ) ; } return expression ; }
Parse ES7 IncrementExpression. IncrementExpression is used instead of ES6's PostFixExpression.

ES7 IncrementExpression[yield]:
1) LeftHandSideExpression[?yield]
2) LeftHandSideExpression[?yield] [[no LineTerminator here]]++
3) LeftHandSideExpression[?yield] [[no LineTerminator here]]--
4) ++LeftHandSideExpression[?yield]
5) --LeftHandSideExpression[?yield]
In TypeScript (2), (3) are parsed as PostfixUnaryExpression. (4), (5) are parsed as PrefixUnaryExpression
Parse ES7 IncrementExpression . IncrementExpression is used instead of ES6 s PostFixExpression .