# trace

#### Availability

Flash Player 4.

#### Usage

    trace(expression)

#### Parameters

`expression` An expression to evaluate. When a SWF file is opened in the Flash authoring tool (via the Test Movie command), the value of the `expression` parameter is displayed in the Output window.

#### Returns

Nothing.

#### Description

Action; evaluates the expression and displays the result in the Output window in test mode.

Use this action to record programming notes or to display messages in the Output window while testing a movie. Use the `expression` parameter to check if a condition exists, or to display values in the Output window. The `trace` action is similar to the `alert` function in JavaScript.

You can use the Omit Trace actions command in Publish Settings to remove `trace` actions from the exported SWF file.

#### Example

This example is from a game in which a draggable movie clip instance named `my_mc` must be released on a specific target. A conditional statement evaluates the `_droptarget` property and executes different actions depending on where `my_mc` is released. The `trace` action is used at the end of the script to evaluate the location of the `my_mc` movie clip, and display the result in the Output window. If `my_mc` doesn't behave as expected (for example, if it snaps to the wrong target), the values sent to the Output window by the `trace` action will help you determine the problem in the script.

    on(press) {
    	my_mc.startDrag();
    }

    on(release) {
    	if(eval(_droptarget) != target) {
    	  	my_mc._x = my_mc_xValue;
    	  	my_mc._y = my_mc_yValue;
    	} else {
    		var my_mc_xValue = my_mc._x;
    		var my_mc_yValue = my_mc._y;
    		target = "_root.pasture";
    	}
    	trace("my_mc_xValue = " + my_mc_xValue);
    	trace("my_mc_xValue = " + my_mc_xValue);
    	stopDrag();
    }