How to loop through an array in react typescript?

Question

How can I loop through an array to display the value?

Here is my following code:

  ineligiblePointsTableRows() {
    return this.state[PointsTableType.INELIGIBLE].contracts.map(contract => {
      return {
          applied: (<input
              value={0}
              disabled
              className="applied-pts-input"
          />),
          reason: (
            <div className="ineligible-reason-container">
              <i className="fa fa-exclamation-triangle"></i>
              <p aria-label={contract.reason}>{contract.reason.map((reason: any, i: any) => (
                <text>Hello world</text>
              ))}</p>
            </div>
          ),
        },
      };
    });
  }

I got error at line contract.reason.map

Object is possibly 'undefined'.ts(2532) (parameter) contract: ContractUsage No quick fixes available

when I console.log(contract.reaons) this is the value:

Array(2)
0: "Cannot borrow usage this far in the future."
1: "Contract has a past due balance."

So my goal is i am trying to loop through contract.reason but I am having error like above. How can I fix this ?

Your error says that contract can be undefined. Have you tried to add an undefined check to it? contract?.reason.map of if(contract !== undefined)contract.reason.map... — J.Stange
– J.Stange, Commented Sep 22, 2021 at 19:05

tomleb · Accepted Answer · 2021-09-22 19:06:33Z

1

It's a typescript error telling you that the object might be "undefined", or in other words, might be empty of any value.

Few possible ways to solve this:

1.

ineligiblePointsTableRows() {
    return this.state[PointsTableType.INELIGIBLE].contracts.map(contract => {
      return {
          applied: (<input
              value={0}
              disabled
              className="applied-pts-input"
          />),
          reason: (
            <div className="ineligible-reason-container">
              <i className="fa fa-exclamation-triangle"></i>
              <p aria-label={contract?.reason}>{contract?.reason?.map((reason: any, i: any) => (
                <text>Hello world</text>
              ))}</p>
            </div>
          ),
        },
      };
    });
  }

ineligiblePointsTableRows() {
    return this.state[PointsTableType.INELIGIBLE].contracts.map(contract => {
      return {
          applied: (<input
              value={0}
              disabled
              className="applied-pts-input"
          />),
          reason: (
            <div className="ineligible-reason-container">
              <i className="fa fa-exclamation-triangle"></i>
              {contract !== undefined && <p aria-label={contract.reason}>{contract.reason.map((reason: any, i: any) => (
                <text>Hello world</text>
              ))}</p>}
            </div>
          ),
        },
      };
    });
  }

answered Sep 22, 2021 at 19:06

tomleb

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2 Comments

Nhan Nguyen Over a year ago

After and question mark for contract and reason like contract?.reason?.map... I got error Property 'map' does not exist on type 'string'.ts(2339)

tomleb Over a year ago

Like the error says, it means that reason is of type string. Can you share what the state looks like?

stolen_orange · Accepted Answer · 2021-09-22 19:06:45Z

1

It means that your contract or contract.reason is possibly undefined. To avoid the error use optional chaining like this:

contract?.reason?.map

answered Sep 22, 2021 at 19:06

stolen_orange

946 bronze badges

3 Comments

Nhan Nguyen Over a year ago

After and question mark for contract and reason like contract?.reason?.map... I got error Property 'map' does not exist on type 'string'.ts(2339)

stolen_orange Over a year ago

It means that reason is actually a string.

stolen_orange Over a year ago

Check the type of reason property

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