In Javascript, how to apply dynamically generated function name
My goal is to efficiently apply a dynamically selected set of transformations to each element of the matrix. I store the selected functions in an array and then apply each one in a single pass through the matrix.
My question is, how can I dynamically create the name of the function that I add to the array of functions?
This fiddle contains my attempt. My question is included in the comment block.
function dynam () {
var prepend = 'before - ';
var append = ' - after';
var whichCase = 'Upper';
var functionsToApply = [];
var matrix = [
['aBc', 'DeF'],
['ghi', 'JKL'],
];
var out = 'Initial: ' + matrix.join(' | ');
document.getElementById('output').innerHTML = out + '\n';
console.log(out);
// Set up transforms
if (whichCase == 'Lower') {
functionsToApply.push(function(v) {return v.toLowerCase();});
} else if (whichCase == 'Upper'){
functionsToApply.push(function(v) {return v.toUpperCase();});
}
// How can the function be defined dynamically?
// Perhaps something like:
// if(['Lower','Upper'].indexOf(whichCase) != -1) {
// functionsToApply.push(function(v) {'return v.to' + which + 'Case();'});
// }
if (prepend && prepend.length > 0 && prepend != 'none') {
functionsToApply.push(function(v) {return prepend + v;});
}
if (append && append.length > 0 && append != 'none') {
functionsToApply.push(function(v) {return v + append;});
}
// Apply all of the transforms to each of the elements of the matrix
matrix = matrix.map(function(row){
return row.map(function(val) {
for (var fn = 0; fn < functionsToApply.length; fn++) {
val = functionsToApply[fn](val);
}
return val;
})
});
out = 'Final: ' + matrix.join(' | ');
document.getElementById('output').innerHTML += out + '\n';
console.log(out);
}
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1 answer
I like to declare my functions in a hash in this case, then you can call them based on the passed value, which is the key to the hash.
Updated: I added a way to dynamically get the bottom / top function and call it.
function dynam(whichCase, prepend, append, matrix) {
var functionHash = {
"Lower" : function(v) {return v.toLowerCase();},
"Upper" : function(v) {return v.toUpperCase();},
"Prepend" : function(v) {return prepend + v;},
"Append": function(v) {return v + append;}
}
// to actually get the case function based on the word passed in,
// you can do it this way.
var lowerUpperFunction = String.prototype['to' + whichCase + 'Case'];
var str = lowerUpperFunction.call("xyz");
console.log(str);
var functionsToApply = [];
var out = 'Initial: ' + matrix.join(' | ');
console.log(out);
// see how we just take the whichCase and make that a call to the hash?
functionsToApply.push(functionHash[whichCase]);
if (prepend && prepend.length > 0 && prepend != 'none') {
functionsToApply.push(functionHash["Prepend"]);
}
if (append && append.length > 0 && append != 'none') {
functionsToApply.push(functionHash["Append"]);
}
// Apply all of the transforms to each of the elements of the matrix
matrix = matrix.map(function(row){
return row.map(function(val) {
for (var fn = 0; fn < functionsToApply.length; fn++) {
console.log("applying function to val" + val );
val = functionsToApply[fn](val);
}
return val;
})
});
out = 'Final: ' + matrix.join(' | ');
return out;
}
var p = 'before - ';
var a = ' - after';
var w = 'Upper';
var m = [
['aBc', 'DeF'],
['ghi', 'JKL'],
];
console.log( dynam(w, p, a, m) );
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