This blog will explore how to resolve the error “Element implicitly has an ‘any’ type because expression of type ‘string’ can’t be used to index in ReactJs”. This is not an error you want to see while developing. It can be really annoying and may stop you from continuing any further. This blog will look at different ways of resolving this issue.

How Does The Error “Element implicitly has an ‘any’ type because expression of type ‘string’ can’t be used to index in ReactJs” Happen?

The following error may occur when you run this code.

plotOptions: {
      name_1: true,
      name_2: true,
}

const plotData: Array<trainInfo> = [{name:"name_1"},{name:"name_2"}].filter(({ name }) =>

However, you may encounter this issue.

Element implicitly has an 'any' type because expression of type 'string' can't be used to 
index type '{ science: null; social: null; math: null; }'. No index signature with a 
parameter of type 'string' was found on type '{ science: null; social: null; math: null; 
}'.

This error occurs when you attempt to use the string name to open the plotOptions property. TypeScript recognizes that a name can have any value, not just the name of a plotOptions property. As a result, TypeScript needs plotOptions to have an index signature so that it understands that any property name can be used in plotOptions. 

How To Handle The Error “Element implicitly has an ‘any’ type because expression of type ‘string’ can’t be used to index in ReactJs”?

Option 1: Change the name type

We recommend changing the name type so that it can only be among the plotOptions properties.

You can now only utilize property names that already appear in plotOptions. You’ll also need to make a minor modification to your code. Firstly, allocate array to a temp variable so that TS knows what type of array it is:

const plotDataTemp: Array<trainInfo> = [ 
    { 
      name: "name_1", 
    }, 
}

Next, filter:

type tplotOptions = {
    [key: string]: boolean
}

const plotOptions: tplotOptions = {
    name_1: true,
    name_2: true,
}

The only manner to type check props at time of compilation if you’re obtaining data from an API is to include an index signature to the plotOptions:

type tplotOptions = { 
    [key: string]: boolean 
}  
const plotOptions: tplotOptions = { 
    name_1: true, 
    name_2: true, 
}

Option 2: Try this

When you use Object.keys, you can try this:

Object.keys(this) 
    .forEach(key => { 
      console.log(this[key as keyof MyClass]); 
    });

Option 3: Utilize object.entries() and append()

The function Object.entries() is used to return an array of the object’s enumerable property [key, value] pairs that are supplied as parameters. The ordering of the properties is the same as what would result from manually looping through the object’s property values.

Excepting two options mentioned above, there is another solution for you to solve the error “Element implicitly has an ‘any’ type because expression of type ‘string’ can’t be used to index in ReactJs”. It is utilizing object.entries() and append(). Look at the followingg code:

Object.entries(data).forEach(item => {
 formData.append(item[0], item[1]);
});

Conclusion

We hope you will enjoy our article about this confusing error. With this knowledge, we know that you can fix your “Element implicitly has an ‘any’ type because expression of type ‘string’ can’t be used to index in ReactJs” error quickly by following these steps! If you still have any other questions about fixing this syntax error, please leave a comment below. Thank you for reading!

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