[Home](./index.md) > [kibana-plugin-plugins-expressions-public](./kibana-plugin-plugins-expressions-public.md) > [ExpressionAstFunctionBuilder](./kibana-plugin-plugins-expressions-public.expressionastfunctionbuilder.md) > [getArgument](./kibana-plugin-plugins-expressions-public.expressionastfunctionbuilder.getargument.md) ## ExpressionAstFunctionBuilder.getArgument property Retrieves an existing argument by name. Useful when you want to retrieve the current array of args and add something to it before calling `replaceArgument`. Any subexpression arguments will be returned as expression builder instances. Signature: ```typescript getArgument: >(name: A) => Array[A] | ExpressionAstExpressionBuilder> | undefined; ```