CODEWITHSUNDEEP
javascriptdesign-patternsconstantsecmascript-3
DanilGholtsman
DanilGholtsman

Reputation: 2374

Constant pattern in Javascript

How were implemened constants in javascript before ES5 was released?

There were no get/set stuff, no writable property, no const word, no Object.freeze stuff as far as I know, so how I could make my own constant, which can't be changed?

Like, as example, Math.PI

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Upvotes: 2

Views: 987

Answers (1)

Bergi
Bergi

Reputation: 664444

How were constant such as Math.PI implemented in javascript before ES5 was released?

Even ES3 knew property attributes - see section 8.6.1 in the spec. There were ReadOnly, DontEnum, DontDelete and Internal.

In fact, for the Math.PI property the spec says "This property has the attributes { DontEnum, DontDelete, ReadOnly }."

However, one could (and still can) overwrite the whole Math object with another one.

How I could make my own constant, which can't be changed?

You could not. There was no way to make variables or objects immutable, for that you needed to wait until ES6 (const) and ES5 (Object.freeze) respectively.

Developer discipline was all that prevented constants from being overwritting. Often, style guides include standards for them, like all-uppercase names.

Upvotes: 5

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