I'm not sure what you are asking makes sense, but functionally in JavaScript lines separated by the ; can be placed on a single line but would be interpreted as individual lines of code.  

var targetName = gs.action.getGlideURI().getMap().get('sysparm_target');
	if (targetName.indexOf('change_request.cmdb_ci') > -1) {

is functionally the same as 

var targetName = gs.action.getGlideURI().getMap().get('sysparm_target');if (targetName.indexOf('change_request.cmdb_ci') > -1) {

but the condition field is not the same field, but is in the same scope, of the script field so would need to use "complete" code in the condition.  However, the targetName variable would be available to the script field.

javascript:var targetName = gs.action.getGlideURI().getMap().get('sysparm_target');if (targetName.indexOf('change_request.cmdb_ci') > -1) { true }

replace the : with a :
it doesn't like the colon lol

if you then say put something like gs.addInfoMessage(targetName) in the script field you would get a message that contained the value of targetName.

I'd really question doing this IN the condition field... not sure the gain.