ngPattern adds the pattern validator to ngModel. It is most often used for text-based input controls, but can also be applied to custom text-based controls.

The validator sets the pattern error key if the ngModel.$viewValue does not match a RegExp which is obtained by evaluating the Angular expression given in the ngPattern attribute value:

• If the expression evaluates to a RegExp object, then this is used directly.
• If the expression evaluates to a string, then it will be converted to a RegExp after wrapping it in ^ and $ characters. For instance, "abc" will be converted to new RegExp('^abc$').