Binder SymbolTable

SymbolTable is implemented as a simple HashMap. Here is the interface (types.ts):

interface SymbolTable {
[index: string]: Symbol;

SymbolTables are initialized by binding. There are a few SymbolTables used by the compiler:

On Node:

locals?: SymbolTable; // Locals associated with node

On Symbol:

members?: SymbolTable; // Class, interface or literal instance members
exports?: SymbolTable; // Module exports

Note: We saw locals getting initialized (to {}) by bindChildren based on ContainerFlags.

SymbolTable population

SymbolTables are populated with Symbols primarily by a call to declareSymbol. This function is presented below in entirety:

* Declares a Symbol for the node and adds it to symbols. Reports errors for conflicting identifier names.
* @param symbolTable - The symbol table which node will be added to.
* @param parent - node's parent declaration.
* @param node - The declaration to be added to the symbol table
* @param includes - The SymbolFlags that node has in addition to its declaration type (eg: export, ambient, etc.)
* @param excludes - The flags which node cannot be declared alongside in a symbol table. Used to report forbidden declarations.
function declareSymbol(symbolTable: SymbolTable, parent: Symbol, node: Declaration, includes: SymbolFlags, excludes: SymbolFlags): Symbol {
// The exported symbol for an export default function/class node is always named "default"
let name = node.flags & NodeFlags.Default && parent ? "default" : getDeclarationName(node);
let symbol: Symbol;
if (name !== undefined) {
// Check and see if the symbol table already has a symbol with this name. If not,
// create a new symbol with this name and add it to the table. Note that we don't
// give the new symbol any flags *yet*. This ensures that it will not conflict
// with the 'excludes' flags we pass in.
// If we do get an existing symbol, see if it conflicts with the new symbol we're
// creating. For example, a 'var' symbol and a 'class' symbol will conflict within
// the same symbol table. If we have a conflict, report the issue on each
// declaration we have for this symbol, and then create a new symbol for this
// declaration.
// If we created a new symbol, either because we didn't have a symbol with this name
// in the symbol table, or we conflicted with an existing symbol, then just add this
// node as the sole declaration of the new symbol.
// Otherwise, we'll be merging into a compatible existing symbol (for example when
// you have multiple 'vars' with the same name in the same container). In this case
// just add this node into the declarations list of the symbol.
symbol = hasProperty(symbolTable, name)
? symbolTable[name]
: (symbolTable[name] = createSymbol(SymbolFlags.None, name));
if (name && (includes & SymbolFlags.Classifiable)) {
classifiableNames[name] = name;
if (symbol.flags & excludes) {
if ( { = node;
// Report errors every position with duplicate declaration
// Report errors on previous encountered declarations
let message = symbol.flags & SymbolFlags.BlockScopedVariable
? Diagnostics.Cannot_redeclare_block_scoped_variable_0
: Diagnostics.Duplicate_identifier_0;
forEach(symbol.declarations, declaration => {
file.bindDiagnostics.push(createDiagnosticForNode( || declaration, message, getDisplayName(declaration)));
file.bindDiagnostics.push(createDiagnosticForNode( || node, message, getDisplayName(node)));
symbol = createSymbol(SymbolFlags.None, name);
else {
symbol = createSymbol(SymbolFlags.None, "__missing");
addDeclarationToSymbol(symbol, node, includes);
symbol.parent = parent;
return symbol;

Which SymbolTable is populated is driven by the first argument to this function. e.g. when adding a declaration to a container of kind SyntaxKind.ClassDeclaration or SyntaxKind.ClassExpression the function declareClassMember will get called which has the following code:

function declareClassMember(node: Declaration, symbolFlags: SymbolFlags, symbolExcludes: SymbolFlags) {
return node.flags & NodeFlags.Static
? declareSymbol(container.symbol.exports, container.symbol, node, symbolFlags, symbolExcludes)
: declareSymbol(container.symbol.members, container.symbol, node, symbolFlags, symbolExcludes);