perf: use Object.assign in @babel/plugin-proposal-object-rest-spread

[layershifter]

Thanks to Mario Baricevic for pointing to this.

🐢 Issue

We use @babel-preset-env to transform our code.

According to .browserslistrc it will compile our code to be used in IE11, there are no support for Object.assign() or object spread and it means that Babel helper will be used. However, we have already required Object.assign() polyfill and it means that we can use it instead of Babel helper.

Example input

const a = { foo: 'bar'}
const b = { baz: 'qux'}
const c = { ...a, ...b }

Example output before

import _objectSpread from "@babel/runtime/helpers/esm/objectSpread";
var a = { foo: 'bar' };
var b = { baz: 'qux' };
var c = _objectSpread({}, a, b);

@babel/runtime/helpers/esm/objectSpread.js contains own implementation which is definitely slower.

Example output with { loose: true, useBuiltIns: true }

var a = { foo: 'bar' };
var b = { baz: 'qux' };
var c = Object.assign({}, a, b);

🏁 Measures

cross-env PERF=true gulp perf --filter *Chat.perf.tsx --times=100

I run the command above 4 times to test changes. During each sample run perf example was run 100 times.

Performance win is around 13%, see results below.

Before

Example	Avg	Median
Chat.perf.tsx (Sample 1)	576.69	575.25
Chat.perf.tsx (Sample 2)	583.62	577.66
Chat.perf.tsx (Sample 3)	588.64	580.58
Chat.perf.tsx (Sample 4)	578.11	575.83
Total	581.765

After

Example	Avg	Median
Example	Avg	Median
Chat.perf.tsx (Sample 1)	504.76	503.9
Chat.perf.tsx (Sample 2)	507.85	505.52
Chat.perf.tsx (Sample 3)	505.25	504.13
Chat.perf.tsx (Sample 4)	513.71	507.39
Total	507.8925

[codecov]

Codecov Report

Merging #1895 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1895   +/-   ##
======================================
  Coverage    69.9%   69.9%           
======================================
  Files         888     888           
  Lines        7775    7775           
  Branches     2244    2244           
======================================
  Hits         5435    5435           
  Misses       2330    2330           
  Partials       10      10

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[layershifter]

Adjusted to have cleaner results.