How to check for an empty/undefined/null string in JavaScript?

1. To check for a truthy value:

if (strValue) {
    // strValue was non-empty string, true, 42, Infinity, [], ...
}

1. To check for a falsy value:

if (!strValue) {
    // strValue was empty string, false, 0, null, undefined, ...
}

1. Empty string (only!)

To check for exactly an empty string, compare for strict equality against "" using the === operator:

if (strValue === "") {
    // strValue was empty string
}

1. To check for not an empty string strictly, use the !== operator:

if (strValue !== "") {
    // strValue was not an empty string
}

1. Using type casting:

if (Boolean(str)) {
    // Code here
}

Typecast the variable to Boolean, where str is a variable.

• It returns false for null, undefined, 0, 000, "", false.

• It returns true for all string values other than the empty string (including strings like "0" and " ")