_exec()	{

		if ( this.codeNode === null ) return this;

		if ( this._needsOutputUpdate === true ) {

			this._value = this.call( 'main' );

			this._needsOutputUpdate = false;

		}

		this._output.value = this._value;

		return this;

	}
Executes the `main` function of the script.

@private
@return {ScriptableNode} A reference to this node.