bug: console.log + pure + minify + JSON.stringify, or even just a template literal

[revelt]

Tested on 0.14.7.

There are three more cases related to console.log on --pure and --minify settings:

---

source index.js:

function test() {
	const obj = { "z": 1 };
	console.log(
		`obj: ${obj}`
	);
}

export { test }

npx esbuild index.js --platform=node --minify --target=node16 --outfile=out.js --pure:console.log

yields out.js:

function o(){`${{z:1}}`}export{o as test};

---

source index.js:

function test() {
	const obj = { "z": 1 };
	console.log(
		JSON.stringify(
			obj,
			null,
			4
		)
	);
}

export { test }

same command,

npx esbuild index.js --platform=node --minify --target=node16 --outfile=out.js --pure:console.log

yields out.js:

function n(){const o={z:1};JSON.stringify(o,null,4)}export{n as test};

---

source index.js:

function test() {
	const obj = { "z": 1 };
	console.log(
		`obj: ${JSON.stringify(
			obj,
			null,
			4
		)}`
	);
}

export { test }

same command,

npx esbuild index.js --platform=node --minify --target=node16 --outfile=out.js --pure:console.log

yields out.js:

function n(){const o={z:1};`${JSON.stringify(o,null,4)}`}export{n as test};

---

[evanw]

Marking a function call as pure means "remove the function call but still evaluate the arguments" so this is expected behavior. The arguments will be preserved if they can't be proven to have no side effects, and esbuild considers running the ToString operation on a variable to be a side effect. I do not consider this to be a bug.

If you want to remove the console.log call entirely (including not evaluating the arguments), marking the function call as pure is not the way to do that. One way to do that is to move the console.log behind a conditional and then use --define to disable the conditional. An example would be doing something like this and then using something like --define:global.NO_LOG=true to remove the call entirely:

!global.NO_LOG && console.log(`obj: ${obj}`);

Closing as working as intended.

[revelt]

Thank you for quick response! It makes sense.