Asynchronous programming keeps remote work from blocking the current flow, then delivers results through callbacks. It suits progressively loaded data, such as an email inbox, but requires careful control of execution order. section 8.1
Manage three recurring problems:
- Create an explicit temporal dependency when one function needs data produced by another. section 8.1
- Avoid deeply nested callbacks, often called a callback pyramid or “Christmas tree of doom.” section 8.1
- Separate asynchronous work from synchronous loops so callbacks retain the intended current record. section 8.1
Passing the current record
const processStudent = student => { if (student.address.country === 'US') { getJSON(`/students/${student.ssn}/grades`, showStudentsGrades(student), handleError); } }; students.forEach(processStudent); section 8.1
Figure 8.4. Passing the current student object as a parameter properly sets the function’s closure and solves the ambiguity resulting from executing remote calls in a loop.
Passing the current student into the callback establishes the intended closure and removes ambiguity during remote calls in a loop. section 8.1
