Promise expression.md

Promise Expression

A String expression of the Promise chain.

Promise Methods

Mapping promise methods to a string expression.

Criteria

Pipeline would always pass the result to the down stream.

Defined methods:

• .then()
• .catch()
• .all()
• .race()

TBD methods:

• .finally()
• .allSettled()

Symbols

• > .then
• # .catch
• && .all
• || .race
• () punctuation

Precedence

The following table lists the precedence symbols. symbols are listed top to bottom, in descending precedence.

Precedence	Symbol	Description
1	()	group the Promise chain
2	> #	Promise then and catch
3	&& ||	Promise All and Race

Example

functions: foo, bar, boo, far

Example 1: foo > bar > boo > far would convert to Javascript

foo()
  .then(bar)
  .then(boo)
  .then(far)

Example 2: foo > bar # boo > far would convert to Javascript

foo()
  .then(bar)
  .catch(boo)
    .then(far)

Example 3: foo && bar > boo > far would convert to Javascript

Promise.all([
  foo(),
  bar()
    .then(boo)
    .then(far)
])

Example 4: (foo && bar) > boo > far would convet to Javascript

Promise.all([
  foo(),
  bar()
])
  .then(boo)
  .then(far)

Example 5: (foo || bar) > boo # far would convert to Javascript

Promise.race([
  foo(),
  bar()
])
  .then(boo)
  .catch(far)

Example 6: (foo > bar) && boo # far would convert to Javascript

Promise.all([
  foo()
    .then(bar),
  boo()
])
  .catch(far)

So symbols precedence looks like (high -> low):

• ()
• >, #
• &&, ||