a minimal react example using plain es5 and webpack with no special configuration (perhaps there should be?) other than source maps.
if the externals section is removed from webpack config, then it takes about 600ms to regenerate dist/bundle.js and dist/bundle.js.map as a consequence of a tiny change in index.js. this is when running webpack --watch and after letting run a few times so that it's warmed up.
a typical output:
Hash: 0ef9b2764bc4b2c1ffa3
Version: webpack 1.13.3
Time: 616ms
Asset Size Chunks Chunk Names
./dist/bundle.js 741 kB 0 [emitted] main
./dist/bundle.js.map 862 kB 0 [emitted] main
[0] ./index.js 220 bytes {0} [built]
+ 177 hidden modules
with react as an external, webpack has almost nothing to do, no source maps to generate, so things are spiffy (~10ms):
Hash: 6c4a658039eb861db41a
Version: webpack 1.13.3
Time: 10ms
Asset Size Chunks Chunk Names
./dist/bundle.js 1.86 kB 0 [emitted] main
./dist/bundle.js.map 2.11 kB 0 [emitted] main
[0] ./index.js 161 bytes {0} [built]
+ 2 hidden modules
yes say that it's 700K or so, with react as an external then your bundle.js is only 700K instead of 1441K and webpack takes only 600ms instead of 1200ms.
yes, the example is meant to demonstrate the save -> reload browser turnaround time.
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