JavaScript

Advanced knowledge about JS

Useful APIs

Deep clone objects

Use new API structuredClone to deep clone the objects.

The best alternative of the old ways:

• Use JSON: JSON.parse(JSON.stringify(obj))
• Use lodash: _.cloneDeep(obj)

const deepCopy = structuredClone(obj)

const shallowCopy = { ...obj }

Performance

JSON.parse is faster than literal objects

Compare the two object assignment statements below, which is faster?

• Literal object:

  const data = { foo: 42, bar: 1337 }; // 🐌
  

• The JSON-stringiefied form:

  const data = JSON.parse('{"foo":42,"bar":1337}'); // 🚀
  

  The JSON.parse is much faster than the literal object above.

  Because the JSON parser is more simple and naive than the Javascript parser.

  A good rule of thumb is to apply this technique for objects of 10 kB or larger

See this V8 blog, and the Chrome Dev Summit 2019

Reference

AST explorer