This method returns the matching index of the specified value in between the specified starting (idx1) and ending index (idx2) within the array. -1 is returned if no match found.
var arrayObj = shell.serviceManager.basics.array;
arrayObj.addValue("a");
arrayObj.addValue("b");
arrayObj.addValue("c");
//this will return -1
var idx = arrayObj.indexOfValueInRange("c", 0, 1);
//this will return 2
idx = arrayObj.indexOfValueInRange("c", 0, 2);