reactjs - array value is undefined … how do I test for that -


javascript array value undefined ... how test that

and

how check not-defined variable in javascript

these wrong far i'm concerned :

i : error

when trying :

console.log(!fromtoparameters[7].value.firstinput); console.log(!!fromtoparameters[7].value.firstinput); console.log(fromtoparameters[7].value.firstinput === undefined); console.log(typeof fromtoparameters[7].value.firstinput == 'undefined'); console.log(fromtoparameters[7].value.firstinput !== undefined); console.log(typeof fromtoparameters[7].value.firstinput != 'undefined');

but (the entry exists) works fine :

console.log(!fromtoparameters[0].value.firstinput); console.log(!!fromtoparameters[0].value.firstinput); console.log(fromtoparameters[0].value.firstinput === undefined); console.log(typeof fromtoparameters[0].value.firstinput == 'undefined'); console.log(fromtoparameters[0].value.firstinput !== undefined); console.log(typeof fromtoparameters[0].value.firstinput != 'undefined');

false true false true false true

is question of react being different js? why can't same in these stackoverflow threads?

update :

so cannot point missing array element @ all.

check answers below.

i think i'll using array.lenght stored in const check increment against within "for" loop allow or disallow modifying array entries on case-by-case basis.

it's annoying can't ask js if damn var of unexisting array index exists or not.

it seems straightforward stuff : can't point index? no. no not variable nor other variable exists @ index. end of.

the guys @ js should put in note adding simple this.

i'm tempted post code have allows me want (calling index lots of undefineds , getting object ""s instead) it's bit monstrous.

you should this:

console.log(fromtoparameters[7] && fromtoparameters[7].value.firstinput); console.log(!!fromtoparameters[7] && fromtoparameters[7].value.firstinput); console.log( fromtoparameters[7]&& typeof fromtoparameters[7].value.firstinput == 'undefined');

i have added check. if fromtoparameters[7] undefined or null, code not break.


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