function-call-spacing 
When calling a function, developers may insert optional whitespace between the function's name and the parentheses that invoke it. The following pairs of function calls are equivalent:
alert('Hello');
alert ('Hello');
console.log(42);
console.log (42);
new Date();
new Date ();Rule Details 
This rule requires or disallows spaces between the function name and the opening parenthesis that calls it.
Options 
This rule has a string option:
- "never"(default) disallows space between the function name and the opening parenthesis.
- "always"requires space between the function name and the opening parenthesis.
Further, in "always" mode, a second object option is available that contains a single boolean allowNewlines property.
never 
Examples of incorrect code for this rule with the default "never" option:
/*eslint @stylistic/js/function-call-spacing: ["error", "never"]*/
fn ();
fn
();Examples of correct code for this rule with the default "never" option:
/*eslint @stylistic/js/function-call-spacing: ["error", "never"]*/
fn();always 
Examples of incorrect code for this rule with the "always" option:
/*eslint @stylistic/js/function-call-spacing: ["error", "always"]*/
fn();
fn
();Examples of correct code for this rule with the "always" option:
/*eslint @stylistic/js/function-call-spacing: ["error", "always"]*/
fn ();allowNewlines 
By default, "always" does not allow newlines. To permit newlines when in "always" mode, set the allowNewlines option to true. Newlines are never required.
Examples of incorrect code for this rule with allowNewlines option enabled:
/*eslint @stylistic/js/function-call-spacing: ["error", "always", { "allowNewlines": true }]*/
fn();Examples of correct code for this rule with the allowNewlines option enabled:
/*eslint @stylistic/js/function-call-spacing: ["error", "always", { "allowNewlines": true }]*/
fn (); // Newlines are never required.
fn
();When Not To Use It 
This rule can safely be turned off if your project does not care about enforcing a consistent style for spacing within function calls.