The ConstrainDOMString dictionary is used to specify a constraint for a property whose value is a string. It allows you to specify one or more exact string values from which one must be the parameter's value, or a set of ideal values which should be used if possible. You can also specify a single string (or an array of strings) which the user agent will do its best to match once all more stringent constraints have been applied.


The value of a ConstrainDOMString can be any of the following:

  • A single DOMString
  • An array of DOMString objects
  • An object with one or both of the following properties:
Either a single DOMString which must be the value of the property, or an array of DOMString objects one of which must be the property's value. If the property can't be set to one of the listed values, matching will fail.
Either a single DOMString or an array of DOMStrings specifying ideal values for the property. If possible, one of the listed values will be used, but if it's not possible, the user agent will use the closest possible match.


Media Capture and Streams
# dom-constraindomstring

Technically, ConstrainDOMString is actually based on an intermediary dictionary named ConstrainDOMStringParameters, which adds exact and ideal to DOMString. However, for the sake of documentation clarity, the intermediate type (present only because of quirks in WebIDL syntax) is ignored here.

Browser compatibility

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See also