Function lowerFirstLetter

lowerFirstLetter convert a OPCUA Identifier to a javascript Identifier

Summary

OPCUA and Javascript use two different rules to build identifiers.

OPCUA Identifier usually starts with a upper case letter and word are join together, this is known as the Pascal case, or CapitalizedWords convention. (for instance HelloWorld) But sometime, OPCUA identifiers do not follow this convention strictly and we can find various other convention being applied such as underscore between word, or addition of ACRONYMIC prefixes. On it's own, this causes great confusion and inconsistency in programming style.

Javascript uses a slightly different convention called camelCase where word are joined together and inner words starts with a capital letter whereas first word starts with a lower case letter. (for instance helloWorld)

In node-opcua we have taken the opinionated decision to consistently use camelCase convention for object properties so that all the code look nice and consistent. the lowerFirstLetter method can be used to easily convert from the OPCUA naming convention to javascript naming convention by applying the following rules.

• each ascii sequence in a identifier will be converted to lower camel case.
• when an identifier only contains upper case letter then it will be untouched. ( i.e CQDF => CQFD) (this rules helps to preserve acronyms)
• when a identifier starts with more than one UpperCase letter but still contain lowercase letter then the first Uppercase letter excluding the last one will be converted to lower case ( ie: EURange = > euRange)
• when a identifier contains several sequences delimited with underscores (_) the above rules will be applied to each of the element of the sequence ( ie: ALM_FlowOutOfTolerance => ALM_flowOutOfTolerance ( ALM=>ALM , FlowOutOfTolerance=>flowOutOfTolerance)

reference:

• https://en.wikipedia.org/wiki/Camel_case
• https://en.wikipedia.org/wiki/Hungarian_notation
• http://wiki.c2.com/?UnderscoreVersusCapitalAndLowerCaseVariableNaming

Example

HelloWorld => helloWorld
 XAxis      => xAxis
 EURange    => euRange
 DATE       => DATE
 XYZ        => XYZ
 AB         => AB
 Ab         => ab
 A          => a
 T1ABC8     => T1ABC8
 F_ABC_D    => F_ABC_D
 ALM_Timeout    => ALM_timeout
 SV_GasOn       => SV_gasOn
 DI_VAL_FlowImp => DI_VAL_flowImp
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