Typescript: Object is possibly 'undefined' while looping Object.keys()

Question

Give this code:

    interface Test {}
    
    interface Config {
        tests?: Record<string, Test>
    }
    
    const config: Config = {
        tests: {
            'test1': 'test1 implementation',
            'test2': 'test2 implementation'
        }
    }
    
    const readConfig = (config: Config) => {
        const testName = 'test1'
        if (config.tests) {
            console.log(config.tests[testName]);
            Object.keys(config.tests).forEach((name) => {
                console.log(config.tests[name]);
            })
        }
    }
    
    readConfig(config);

If I try to access the config.tests[testName] immediately in the if block then it works fine. However I'm getting "Object is possibly 'undefined'." on this line, even though I check for undefined above in the if condition.:

console.log(config.tests[name]);

You can assert the value is present like so: console.log(config.tests[name]!); note the bang ! operator — jsonderulo
– jsonderulo, Commented Jul 8, 2021 at 8:01

CertainPerformance · Accepted Answer · 2021-07-08 03:03:11Z

2

Try putting the tests into its own identifier first.

const readConfig = (config: Config) => {
    const testName = 'test1';
    const { tests } = config;
    if (tests) {
        console.log(tests[testName]);
        Object.keys(tests).forEach((name) => {
            console.log(tests[name]);
        })
    }
}

You also might want to use Object.entries to get both the key and value at once - or just Object.values if you only need the value.

Object.entries(tests).forEach((name, value) => {
    console.log(value);
})

answered Jul 8, 2021 at 3:03

CertainPerformance

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1 Comment

Sergiu Cosciug Over a year ago

Object.entries(tests).forEach(([name, value]) => { console.log(name, value); }) works best in my case

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