String coercion syntax failing (variable += "") #85789
Description
Link to the code that reproduces this issue
https://codesandbox.io/p/devbox/jvhqgh
To Reproduce
d3-hierarcy uses string coercion syntax that fails in Next v16 + React v19. The bug was originally reported here d3/d3#4064.
The nodeId += "" syntax is used here: https://github.com/d3/d3-hierarchy/blob/c4ae7066d5a52e8aeaab24b3f7113e25c38183f2/src/stratify.js#L53
For some reason using this syntax fails the check where as using string template syntax succeeds.
nodeId += "" -> fails
nodeId = `${nodeId}` -> succeeds
Example code:
const data = [
{ id: "root", parentId: "", size: null },
{ id: "a", parentId: "root", size: 10 },
{ id: "b", parentId: "root", size: 20 },
];
var nodes = Array.from(data),
currentId = (d) => d.id,
currentParentId = (d) => d.parentId,
n,
i,
nodeId;
for (i = 0, n = nodes.length; i < n; ++i) {
if ((nodeId = currentId(data[i])) != null && (nodeId += "")) {
console.log("passed 1");
}
if ((nodeId = currentParentId(data[i])) != null && (nodeId += "")) {
console.log("passed 2");
}
}
for (i = 0, n = nodes.length; i < n; ++i) {
if ((nodeId = currentId(data[i])) != null && (nodeId = `${nodeId}`)) {
console.log("passed 3");
}
if ((nodeId = currentParentId(data[i])) != null && (nodeId = `${nodeId}`)) {
console.log("passed 4");
}
}Current vs. Expected behavior
Running the example code, I expect all 4 conditions to log to the console.
Provide environment information
Operating System:
Platform: linux
Arch: x64
Version: #1 SMP PREEMPT_DYNAMIC Sun Aug 6 20:05:33 UTC 2023
Available memory (MB): 4102
Available CPU cores: 2
Binaries:
Node: 20.12.0
npm: 10.5.0
Yarn: 1.22.19
pnpm: 8.15.6
Relevant Packages:
next: 16.0.1 // Latest available version is detected (16.0.1).
eslint-config-next: 15.2.0
react: 19.2.0
react-dom: 19.2.0
typescript: 5.8.3
Next.js Config:
output: N/AWhich area(s) are affected? (Select all that apply)
Not sure
Which stage(s) are affected? (Select all that apply)
next dev (local), next build (local), next start (local), Vercel (Deployed), Other (Deployed)
Additional context
No response