TS2451: Cannot redeclare block-scoped variable 'custom' - node.js

Question

I'm using typescript in a web project. I use awesome-typescript-loader as a webpack loader. I am getting error when building my project:
ERROR in [at-loader] ./node_modules/#types/node/index.d.ts:82:15
TS2451: Cannot redeclare block-scoped variable 'custom'.
ERROR in [at-loader] ./node_modules/#types/node/index.d.ts:85:15
TS2451: Cannot redeclare block-scoped variable 'custom'.
ERROR in [at-loader] ./node_modules/#types/node/ts3.2/util.d.ts:7:15
TS2451: Cannot redeclare block-scoped variable 'custom'.
ERROR in [at-loader] ./node_modules/#types/node/ts3.2/util.d.ts:10:15
TS2451: Cannot redeclare block-scoped variable 'custom'.
I initiated a complete new folder with just typescript and #types/typescript installed, I can still see the same error complained by visual studio code.
Versions below:
"dependencies": {
"#types/node": "^11.13.6",
"typescript": "^3.4.4"
}
As the error showed above, I found
in index.d.ts:
declare module "util" {
namespace inspect {
const custom: symbol;
}
namespace promisify {
const custom: symbol;
}
namespace types {
function isBigInt64Array(value: any): boolean;
function isBigUint64Array(value: any): boolean;
}
}
in util.d.ts:
declare module "util" {
namespace inspect {
const custom: unique symbol;
}
namespace promisify {
const custom: unique symbol;
}
namespace types {
function isBigInt64Array(value: any): value is BigInt64Array;
function isBigUint64Array(value: any): value is BigUint64Array;
}
}
We can see custom is indeed being re-declared in index.d.ts and util.d.ts.
So my question is how to fix this issue? Is this a bug of #types/node?

Answer 1

I was facing the same issue. Removing reference to node in tsconfig fixed the issue for me.
Sample tsconfig.
{
"compilerOptions": {
"target": "es6",
"module": "commonjs",
"outDir": "dist",
"sourceMap": true
},
"files": [
// "./node_modules/#types/node/index.d.ts",
"./node_modules/#types/express/index.d.ts"
],
"include": [
"src/**/*.ts"
],
"exclude": [
"node_modules"
],
"lib": [
"es2017"
]
}

Answer 2

My problem is that I accidentally included node_modules/#types. Fixed by comment it out like this:
"include": ["src/**/*.ts","__tests__/**/*.ts"/*, "node_modules/#types"*/]

Answer 3

I had the same issue, but the error message was misleading just because of something wrong cached. I tried many things, but finally solved it by removing npm_modules, clearing cache, and new installation:
npm cache clean --force
npm install

Answer 4

I added this piece of code twice in protractor.conf.js file
require('ts-node').register({
project: require('path').join(__dirname, './tsconfig.e2e.json')
});