[Home](./index.md) > [kibana-plugin-plugins-expressions-server](./kibana-plugin-plugins-expressions-server.md) > [ExpressionAstFunctionBuilder](./kibana-plugin-plugins-expressions-server.expressionastfunctionbuilder.md) > [addArgument](./kibana-plugin-plugins-expressions-server.expressionastfunctionbuilder.addargument.md) ## ExpressionAstFunctionBuilder.addArgument property Adds an additional argument to the function. For multi-args, this should be called once for each new arg. Note that TS will not enforce whether multi-args are available, so only use this to update an existing arg if you are certain it is a multi-arg. Signature: ```typescript addArgument: >(name: A, value: FunctionArgs[A] | ExpressionAstExpressionBuilder) => this; ```