Author: John Au-Yeung

Web developer specializing in React, Vue, and front end development.

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React Answers

How to get checkbox value in React.js?

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To get checkbox value in React.js, we can use a state.

For instance, we write

const Component = () => {
  const [value, setvalue] = useState(false);

  return (
    <div className="form-check">
      <input
        className="form-check-input"
        checked={value}
        onChange={(e) => setValue(e.target.checked)}
        type="checkbox"
      />
      <label className="form-check-label">chechbox value</label>
      {value}
    </div>
  );
};

to set the onChange prop of the checkbox input to a function that calls setValue with the checked value of the checkbox.

Then we get the checked value from the value state and set that as the checked prop’s value to update the checkbox with the latest checked value.

Categories
JavaScript Answers

How to create a new file with JavaScript?

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To create a new file with JavaScript, we use the File constructor.

For instance, we write

const f = new File([""], "filename");

to call File with an array with the file contents and a string with the filename respectively.

We can pass in a third argument with some options.

For example, we write

const f = new File([""], "filename.txt", {
  type: "text/plain",
  lastModified: date,
});

to call File with an object with the MIME type and the lastModified date of the file as the 3rd argument.

Categories
TypeScript Answers

How to fix the ‘ts2769: no overload matches this call.’ error with TypeScript?

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To fix the ‘ts2769: no overload matches this call.’ error with TypeScript, we should call a function with the arguments that matches one of the signatures of the function.

For instance, we write

function foo(str: "hello"): string;
function foo(str: "world"): string;
function foo(str: "hello" | "world"): string {
  return str;
}

foo("hello");

to define the foo function with multiple signatures.

It accepts the str parameter which can be either 'hello' or 'world'.

And then we call foo with 'hello' to we avoid the error.

If we call foo with something other than 'hello' or 'world', then we get this error.

Categories
React Answers

How to fix ‘a component is changing an uncontrolled input to be controlled. This is likely caused by the value changing from undefined to a defined value, which should not happen. Decide between using a controlled or uncontrolled input element for the lifetime of the component.’ error with React?

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To fix ‘a component is changing an uncontrolled input to be controlled. This is likely caused by the value changing from undefined to a defined value, which should not happen. Decide between using a controlled or uncontrolled input element for the lifetime of the component.’ error with React, we should make sure the value prop of the input is always set to a value.

For instance, we write

<input value={inputValue} />

to add an input with the value prop set to the inputValue state or prop.

We should make sure inputValue is never null or undefined to avoid this error.

Categories
JavaScript Answers

How to fix referenceerror: localstorage is not defined with JavaScript?

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To fix referenceerror: localstorage is not defined with JavaScript, we should make sure we spell it correctly and only try to use it in the browser environment.

For instance, we write

const foo = localStorage.getItem("foo");

to call localStorage.getItem with 'foo' to return the value of the local storage entry with key 'foo'.

And we write

localStorage.setItem("foo", 1);

to call setItem to set the item with key 'foo' to value 1.

And we write

localStorage.removeItem("foo");

to call removeItem to remove the item with key 'key'.

We should only try to use these methods in code that runs in the browser.