ConstrainDouble - Web APIs 编辑

The ConstrainDouble type is used to specify a constraint for a property whose value is a double-precision floating-point number. It extends the DoubleRange dictionary (which provides the ability to specify a permitted range of property values) to also support an exact value and/or an ideal value the property should take on. Additionally, you can specify the property's value as a simple floating-point value, in which case the user agent does its best to match the value once all other more stringent constraints are met.

Properties

If the value of a ConstrainDouble is an object rather than a number, it may have the properties below in addition the properties it inherits from DoubleRange.

exact

A double-precision floating-point number specifying a specific, required, value the property must have to be considered acceptable.

ideal

A double-precision floating-point number specifying a value the property would ideally have, but which can be considered optional if necessary to find a match.

Specifications

Technically, ConstrainDouble is actually based on an intermediary dictionary named ConstrainDoubleRange, which adds exact and ideal to DoubleRange, with ConstrainDouble being a type that can be either a long integer or a DoubleRange. 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

• Media Capture and Streams API
• Capabilities, constraints, and settings
• DoubleRange
• MediaTrackConstraints
• MediaTrackCapabilities
• MediaTrackSupportedConstraints