为何TypeScript编译器未检测到可选属性调用toFixed()的错误？

我在VS Code中编写了如下TypeScript代码：

function car (car: {
    make: string,
    model: string,
    year: number,
    chargeVoltage?: number
}){
    console.log(`${car.model} was made by ${car.make} in year ${car.year} ${car.chargeVoltage.toFixed(2)}`)
}

car({
    make: 'Ford',
    model: 'Fortuner',
    year: 1997
})

问题在于，chargeVoltage是可选属性，直接调用其toFixed()方法时，TypeScript编译器未抛出类型错误，仅在运行时出现报错。这类空值调用错误本应在编译阶段就被捕获。

以下是我的项目配置文件：

package.json #

{
  "name": "typescript",
  "version": "1.0.0",
  "description": "Repo focussed on learning typescript",
  "main": "src",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "dev": "tsc --watch --preserveWatchOutput"
  },
  "author": "Atul Singh",
  "license": "ISC",
  "dependencies": {
    "nodemon": "^2.0.22",
    "tsc": "^2.0.4",
    "typescript": "^5.1.6"
  },
  "devDependencies": {
    "concurrently": "^8.2.0",
    "ts-node": "^10.9.1"
  }
}

tsconfig.json #

{
    "compilerOptions": {
        "target": "ES2017", // which level of js support to target
        "outDir": "dist",    // where to put the ts file
       
    },
    "include": ["src"]
}

TypeScript默认未开启严格空值检查规则，因此对于可能为undefined的可选属性，编译器不会强制要求你处理空值场景。要让编译器捕获这类错误，需在tsconfig.json中启用严格模式或单独开启strictNullChecks选项。

1. 修改tsconfig.json配置 #

更新compilerOptions，添加strict: true（推荐，开启所有严格检查规则），或单独设置strictNullChecks: true：

{
    "compilerOptions": {
        "target": "ES2017",
        "outDir": "dist",
        "strict": true // 开启严格模式，包含strictNullChecks
        // 或单独启用："strictNullChecks": true
    },
    "include": ["src"]
}

开启后，编译器会直接提示chargeVoltage可能为undefined，无法直接调用toFixed()方法。此时你需要通过以下方式处理空值：

2. 空值处理方案 #

• 可选链操作符+默认值：

console.log(`${car.model} was made by ${car.make} in year ${car.year} ${car.chargeVoltage?.toFixed(2) || 'N/A'}`)

• 提前判断属性存在性：

const voltageText = car.chargeVoltage ? car.chargeVoltage.toFixed(2) : '无电压数据';
console.log(`${car.model} was made by ${car.make} in year ${car.year} ${voltageText}`)

• 空值合并运算符设置默认值：

function car (car: {
    make: string,
    model: string,
    year: number,
    chargeVoltage?: number
}){
    const voltage = car.chargeVoltage ?? 0; // 若属性不存在则默认设为0
    console.log(`${car.model} was made by ${car.make} in year ${car.year} ${voltage.toFixed(2)}`)
}

内容的提问来源于stack exchange，提问作者Atul