# Binder Error Reporting

Binding errors are added to the sourceFile's list of `bindDiagnostics`.

An example error detected during binding is the use of `eval` or `arguments` as a variable name in `use strict` scenario. The relevant code is presented in its entirety below (`checkStrictModeEvalOrArguments` is called from multiple places, call stacks originating from `bindWorker` which calls different functions for different node `SyntaxKind`):

```typescript
function checkStrictModeEvalOrArguments(contextNode: Node, name: Node) {
    if (name && name.kind === SyntaxKind.Identifier) {
        let identifier = <Identifier>name;
        if (isEvalOrArgumentsIdentifier(identifier)) {
            // We check first if the name is inside class declaration or class expression; if so give explicit message
            // otherwise report generic error message.
            let span = getErrorSpanForNode(file, name);
            file.bindDiagnostics.push(createFileDiagnostic(file, span.start, span.length,
                getStrictModeEvalOrArgumentsMessage(contextNode), identifier.text));
        }
    }
}

function isEvalOrArgumentsIdentifier(node: Node): boolean {
    return node.kind === SyntaxKind.Identifier &&
        ((<Identifier>node).text === "eval" || (<Identifier>node).text === "arguments");
}

function getStrictModeEvalOrArgumentsMessage(node: Node) {
    // Provide specialized messages to help the user understand why we think they're in
    // strict mode.
    if (getContainingClass(node)) {
        return Diagnostics.Invalid_use_of_0_Class_definitions_are_automatically_in_strict_mode;
    }

    if (file.externalModuleIndicator) {
        return Diagnostics.Invalid_use_of_0_Modules_are_automatically_in_strict_mode;
    }

    return Diagnostics.Invalid_use_of_0_in_strict_mode;
}
```


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