null or undefined check should be consistent for all accesses of a variable

• INSUFFICIENT_NULL_CHECK
• Error
• Medium
• No tags

This rule applies when a variable is checked for null (or undefined) value at one point but is accessed without null check at another point.

If the variable has indeed null value, a TypeError exception occurs when trying to access its property or call it as a function.

Therefore, a programmer needs to check the following:

• Access a variable consistently after checking it is not null.
• Remove all null checks of a variable consistently if it cannot be null.

Noncompliant Code Example

function example1(x) {
    x.p = 42;
    if (x != null) { // INSUFFICIENT_NULL_CHECK alarm
        doSomething(x);
    }
}

function example2(x) {
    if (x != null) { // INSUFFICIENT_NULL_CHECK alarm
        doSomething(x);
    }
    y = x.p;
}

function example3(cb) {
    cb();
    if (cb != null) { // INSUFFICIENT_NULL_CHECK alarm
        doSomething(cb);
    }
}

Compliant Code Example

function example1(x) {
    if (x != null) {
        x.p = 42;
        doSomething(x);
    }
}

function example2(x) {
    if (x != null) {
        doSomething(x);
    }
    y = x != null ? x.p : '';
}

function example3(cb) {
    // If 'cb' must not be null
    cb();
    doSomething(cb);
}

Version

This rule was introduced in DeepScan 1.0.0-alpha.