Why is "123abc" considered a number is javascript

I am trying to validate an input field so that it only accepts numbers.

When I try to validate an input such as ‘123’ it works as expected, however when I validate an input such as ‘123abc’ it does not work and ‘123abc’ gets accepted as a number.

Could any please explain to me why and what to do about it?

My code is in the following codepen link: https://codepen.io/npinak/pen/dygNEOW?editors=1011

// get the operator button class
const operators = Array.from(document.getElementsByClassName('operator'))

// add function to each button
operators.forEach((operator) => {
    operator.addEventListener('click', mathOperation)
})

// values from input fields
const inputs = Array.from(document.getElementsByClassName('input'))

// check for blank inputs 
function blankInput(e){

    const textValue = e.target.value
    const allSpacesRemoved = textValue.replace(/ /g, '');
    const allSpacesRemovedFloat = parseFloat(allSpacesRemoved)
    
    if (allSpacesRemovedFloat === ''){
        e.target.classList.add('noInput')
    } else if (Number.isNaN(allSpacesRemovedFloat) === true){
        console.log(Number.isNaN(allSpacesRemovedFloat))
        e.target.classList.add('noInput')
    } else {
        e.target.classList.remove('noInput')
    }
}

console.log(inputs[0])

inputs.forEach((input) => {
    input.addEventListener('blur', blankInput)
})


function mathOperation(e){

    e.preventDefault()
    // get header for result
    const result = document.getElementById("result")

    // convert values from input to float
    const value1 = parseFloat(inputs[0].value)
    const value2 = parseFloat(inputs[1].value)

    //check if value1 and value2 are numbers
    if (Number.isNaN(value1) || Number.isNaN(value2)){
        window.alert("Please enter a valid input.")
        
        // get input element

        // add .inputVisible class

        // remove .inputVisible class after 3 seconds 
        return 
    }

    // math operation
    if(e.srcElement.id === 'division'){
        const finalValue = value1 / value2
        result.innerText = finalValue
    } else if (e.srcElement.id === 'multiplication') {
        const finalValue = value1 * value2
        result.innerText = finalValue
    } else if (e.srcElement.id === 'subtraction') {
        const finalValue = value1 - value2
        result.innerText = finalValue
    } else if (e.srcElement.id === 'addition') {
        const finalValue = value1 + value2
        result.innerText = finalValue
    }
}```